I'm really enjoying the thread on stuff your OH does that makes you cringe, so I thought I'd reverse it!
I'll start: I enjoy rearranging fruit in the supermarket into the shape of willies (such as a cucumber and two peaches).
I will sometimes serenade him in the street, but just with songs I've made up, mostly based on observational stuff a la Randy Newman (I don't think he'd mind so much if they were actual songs).
Sometimes in restaurants, I read the menu out loud to him in an appalling French accent.
I like to have a sly fart and blame it on the cats, even when the cats aren't there.