I'm going to joke around with my friend about a guy who likes her
Is there something to be funny about?
It is just all fun and games.
You shouldn't make fun of your friend and embarrass him in front of others for your pleasure. He'd be hurt if you did so.
I'll tell him that it's just a joke, he doesn't have to be serious
You shouldn't do this. You finding it funny is irrelevant. You are hurting your friend for entertainment.