Yeah, but what if you make a mistake and they don't like it? Then you just used someone else's money to buy something they never asked for. If you are going to use someone else's money for something they can't choose, I think that trying to make them laugh with low stakes silly antics is better than acting like you respect someone without directly asking their preferences.

That's just my initial reaction. Different people have different relationships, and all's well that ends well.