How acceptable is "asinine"

Asinine means ‘extremely stupid or foolish’ and is perfectly acceptable in a school context. It has nothing to do with arse, if that’s what you’re thinking.

I tend to notice, and not only in English, a tendency to use certain pejoratives based on the assumption as to whether the object of the chosen word would be assumed to understand its meaning. There is not necessarily any relation between that phenomenon and the physical presence of said object, but maybe the underlying thought is that, although we spoke our mind about them, even if they heard they would not take offence and possibly resort to non-verbal retorts.

Of course, this tactic can heavily backfire when the object of the pejorative understands 'asinine' to mean 'like an arse' rather than 'like a donkey'...

To actually answer the question, I'd say that the use of asinine would be quite acceptable, as long as the (intended) audience actually understands its meaning. This, however, holds true for almost any part of speech that could or would be construed by the audience as slang, jargon or simple obfuscation ("look at them guys wi' all of 'm fancy words!").

I have yet to see anyone get in trouble for using the word "asinine". Depending on the kind of essay you're writing, it's probably fine. However, if you are arguing a point, calling the opposition asinine is usually considered ad-hominem, and not acceptable.

I got in trouble for using it in court today (I’m a lawyer), the judge told me to “watch my language a little bit”.