"Dude, your breath is rank! As a friend I suggest you do something about it. Mints, gum, brushing after every meal, I don't know what would work best for you, but something needs to be done."
Remember, for some people bad breath can be a medical condition and they need to seek professional support for treatment options. But, if your friend just has bad hygiene then just be straight with them. That's what friends are for. 🙂
Edit: It's kinda funny your asking this question with what you've put in your signature line.