Anything that's asinine is truly stupid or foolish. Your brother might love a ridiculous reality TV show, while you find it completely asinine.
Asinine derives from the Latin asinus, which means "stupid," but also "like an ass or donkey." Asinine behavior isn't simply dumb, but is as obstinate and lacking in judgement as a stubborn donkey. It would be foolish if your friend spray-painted graffiti on the neighbor's garage door, but it would be asinine if he also signed his name.