Here's the shortest answer you'll ever get from us: You can't. Unless you're a teacher, pointing out a fallacy just makes you look like a logical bully. Or, worse, a logician.
Correcting a fallacy is like correcting someone's grammar: Unless you're a teacher or parent, just let it slide. Rhetoric teaches you that winning an argument means winning over people, not just scoring points. It means getting your audience to like and trust you. Being a logic snob does not make you likable.
On the other hand, what if you have a ready audience besides your illogical friend? In that case, you can try taking the fallacy literally and following it to its hilarious end. You may get a laugh. Even from your friend, if he's a good sport.
We made this video with an example from our favorite logician, Homer Simpson.