Then lay it on him straight.
Just say, "You know dude (or whatever his name is), I’m your friend, but I gotta tell you that your breath really wreaks. When you’re talking, sometimes it’s hard to concentrate on what you’re saying because all I can think about is giving you a breath mint. Are you brushing your teeth? Maybe you should brush more often. If you’re brushing, then you should go see a dentist because you probably have a rotten tooth. You can go to the dental school if you can’t afford it, they’ll give you a discount. Other people feel the same way, and, it’s bad, dude! I wouldn’t say something unless it was foul! You’re my friend and I don’t want to offend you, but I just can’t ignore it anymore. Here’s some mints, and a toothbrush."