I don't get why most of the comments are steering you away from this. It's the same thing as meeting someone at a bar for the first time and having sex the same night. This is tricky, as I've never done this before myself but...maybe ask for his number? Questions like this are easier to ask over text. So you can start it off like, "You wanna hear smth funny? Maybe a bit crazy?" Keep it light-hearted so that you both can laugh it off if it goes to ****. Oh, and also. be ready to be the talk of the class or school, because he will definitely let his friends know a random girl just asked to give him a *******. Most guys would be down for it though, honestly, as long as you don't look/act disgusting.