zany
Very silly, wild, and funny in a strange way.
Zany means amusingly unconventional, wildly silly, or entertainingly unpredictable. A zany comedian might wear ridiculous costumes, make absurd faces, and create chaos on stage just to get laughs. A zany character in a movie does unexpected, over-the-top things that surprise the audience.
The word comes from zanni, a type of comic servant character in old Italian theater who would stumble around, play practical jokes, and generally act foolish to entertain crowds. Today, zany describes anything hilariously offbeat or eccentric.
Think of the difference between regular funny and zany: telling a good joke is funny, but showing up to school dressed as a giant banana and speaking only in rhymes would be zany. Zany humor is physical, exaggerated, and a little wild. The Marx Brothers were famous for their zany antics in classic films, creating elaborate schemes and causing mayhem wherever they went.
When you call someone's idea zany, you might mean it's creative and delightfully weird, though sometimes it hints that the idea is too wild to work. A zany plan to train squirrels to deliver mail might be imaginative, but probably not practical.