An antic is a prank to the extreme. It’s outrageous, but it’s usually meant to be funny. When the senior class steals the principal’s car and manages to get it inside the gym, the antic may be condemned by the school, but everyone else probably thinks it’s hilarious.
The noun antic is most commonly used in the plural form, as in “the coach was growing tired of his star player’s silly antics after scoring.” Sometimes antics can lean toward the not-so-funny side as well. Really ridiculous behavior, that is more foolish than funny, can also be called antics. Antic can also be used an as adjective, as in "her antic stand-up routine had everyone rolling in the aisles." It more infrequently can be used as a verb meaning basically "to act like a clown."