Dtyjlui

How about plain old Do not? It's not sexy, but it gets the point across unambiguously.

I'm jumping in with an edit...

Avoid setting the cat/house on fire.

Shun setting the cat/house on fire.

Abstain from setting the cat/house on fire.

Do not set the cat/house on fire.

Not sure how strong you want to be here, but, eschew is pretty strong.

From MW eschew:

eschew v.

to avoid habitually on moral or practical grounds

The expression to steer clear of something or someone sounds stronger, I think. It's oftentimes used in situations where you're advised to avoid something that can be very dangerous for you. Somebody advising you against doing drugs would be one good example. The following is how the Cambridge Dictionary defines this expression:

to avoid someone or something that seems unpleasant, dangerous, or likely to cause problems

Example sentence:

They warned their children to steer clear of drugs.

The phrasing "Avoid <noun>" implies physically avoiding contact with it. It may be necessary to replace the noun (in the example "macaroni and cheese") with a verb phrase clarifying the activity you want to be avoided (presumably eating in this case).

In any case, if you are going to introduce a verb phrase, it would be better to just say "Do not <verb>...".

"Avoid macaroni and cheese" - Ambiguous. Should I just not be in the same room as macaroni and cheese?

"Avoid eating macaroni and cheese" - Better, but still not an absolute command.

"Do not eat macaroni and cheese" - Most direct

Although this would make the phrase longer, I would suggest adding some modifiers to avoid to make it firmer. Use modifiers which emphasize you should not even be considering whatever you're avoiding. Here are some examples:

Completely avoid alcohol.

Strictly avoid alcohol.

Avoid alcohol at all costs.

Note: this answer was edited with suggestions from the commenters, as some of the previous phrases were non-idomatic. Thanks Eric Wofsey and user568458!

Abstain

restrain oneself from doing or enjoying something

While abstaining, a person consciously restrains himself from taking pleasure.

E.g.

"she intends to abstain from sex before marriage"

Using NO is a viable and ideal 'stronger' and 'shorter' alternative to 'avoid'.

No Swimming

No Smoking

No Entry

It is unambiguous and authoritative.

NO means NO.

The best solution is often the simplest.

Use do not [verb].

Anglophone culture, especially formal Anglophone culture, thinks of direct commands and blunt statements as being rude. A sentence like do not eat macaroni and cheese contains the forcefulness you want, but it's also blunt in a way that's unacceptable in certain contexts.

This is less true today, what with the trend of modern Anglophone culture towards informality, but it's not gone. This is what makes avoid useful. Unlike do not, avoid is a suggestion, not a command. Do not requires an explicit verb, avoid can leave the verb unstated. The reason avoid seems so soft is because seeming soft is the entire point!

The same applies to eschew, abstain from, and all other formal words. Just compare:

Avoid murder.

Eschew murder.

Abstain from murder.

Do not murder.

Use do not if you want force. Everything else is just an elaborate way to avoid having that force.

Along the lines of "abstain" is also the word "refrain", though again, you would still need to add "from" + an action.
Eg. Refrain from eating macaroni and cheese.

Alternatively, "reject" or "refuse" could work, especially if one expects to be offered macaroni and cheese often or have it around a lot. "Forsake" is an option too (though uncommon parlance), with a bit more permanent implications. To "forsake macaroni" might be some moral or expected-to-be-permanent rejection of the food, perhaps if one was going vegan. None of these three would require a verb, and all would go directly before the noun.

I propose Reject

dismiss as inadequate, unacceptable, or faulty.

I find it has connotations of purposefulness, forcefulness and determination.

You aren't just steering away from mac and cheese, if you come into contact you'll proactively push it away.

"Little Jimmy rejected the proffered bowl; shoving it on the floor. Mac-n-cheese was the worst!"

If you're OK with a distinctly old-testament flavour:

abhor

regard with disgust and hatred.

This might be an interesting choice as it does not command the desired action directly, but rather the state of mind from which the action naturally flows.

In income tax terminology, evade is a much stronger word than avoid. In fact, avoiding taxes is legal and evading taxes is illegal.

An example of avoiding taxes is to have paid some medical bills in 2018 which were not due until 2019. The floor on the medical tax deduction for 2018 is 7.5%, as opposed to 10% for 2019. Of course the calculation is not this simple, and you would have to take into account what your medical bills were in 2018 versus what they are likely to be in 2019. But this is legal, and avoiding taxes is recommended by CPAs. (If you didn't do this already, it is too late.)

An example of evading taxes is to not report income or to overstate deductions. For example to "make a mistake" by overstating your charitable deductions. There are many sophisticated ways to evade taxes, and they are illegal.

See, for example What is the difference between tax avoidance and tax evasion. I will not quote from this article, because it would only verify what I said above, not significantly add to it.

Whether you can take this distinction and apply it to diet busting foods like chocolate cream pie a la mode is problematical.

Two more options for you:

One could offer the command to "cut out" alcohol/macaroni/slovenliness/whatever. By evoking an image of excising something that's unwanted or dangerous, this phrase communicates intentionality as well as thoroughness. It seems most appropriate when the undesirable behavior/environment is already present, however, which is not always the case.

"Repudiate" could also be a good choice if the avoidance involves taking an overt stance on something. It's sometimes used to indicate verbally rejecting something (and quite strongly), but with such wholeheartedness that one refuses to be associated (positively) with the thing being rejected.

I agree with @Robusto that shun is the simplest and therefore in most situations the best. All the alternatives I can think of are slightly (or very) anachronistic.

That said, spurn - while a little old-fashioned - adds an extra note of active disdain.

spurn v.

to reject with contempt

You could go for a warning instead of (or in addition to) an advice.

beware

To be on guard against; be cautious of: "Beware the ides of March" (Shakespeare).

From there we get such warnings as:

• Beware macaroni and cheese and its users


• Be cautious of macaroni and cheese and its users


• Be extremely wary of macaroni and cheese and its users


• Exercise extreme caution in the vicinity of macaroni and cheese or its users

Which can be coupled to an (embellished) advice such as:

• avoid like the plague


• keep your distance at all costs


• maintain a distance of at least 10 m or suffer certain death

I have received the advice for programming, where the recommendation to "avoid" is usually intended to have much stronger connotation, to use the word must, as in "You must avoid mac & cheese," or "You must not eat mac and cheese."

Several options off the top of my head:

• avert


• fend off


• abstain


• desist


• refrain

How about never ever...!? I.e. as in Never ever touch drugs!

Exclamation mark is an additional way to make it stronger.

It's also possible to make it a commandment and add some solemnity:

You shall never ever touch drugs!

Just for completeness sake: (from Dictionary.com)

Abjure ab·jure /abˈjo͝or,əbˈjo͝or/ v. FORMAL

solemnly renounce (a belief, cause, or claim).

I personally like the following best, which have have connotations of avoid, but with more force:

• 
  eschew (formal)


• 
  abstain from (slightly formal)


• 
  evade (although it has the implication that the avoidance is more "active")


• shun

Equally suitable is an adverb or adverbial phrase attached to avoid or one of its near-synonyms. E.g., absolutely/wholeheartedly avoid or avoid like the plague (as trite a simile as it is!) would work well.

Of course, the choice should always be dependent on the context and the specific use...

circumnavigate

1. to go or maneuver around


2. to sail or fly around; make the circuit of by navigation

"I carefully circumnavigated the dead bird on the sidewalk."

There's another answer which nobody has mentioned (though this use is a little archaic):

Despise

Merriam-Webster lists the definition as:

to look down on with contempt or aversion

The usual use is contempt, but it's certainly possible to use it as "Despise macaroni and cheese" meaning "Avoid macaroni and cheese", and as an imperative it'll be more easily understood that way. Again, though, I'm pretty sure it's archaic so YMMV.