each and everytime u see him, offer him breath mints after the first minutes of conversation. or u cud pretend to ask if he's alright one day, and tell him ur breath smells funny, maybe he has halitosis or something(some other medical condition), he shud go and have it checked out. or the classic, share a story about 'a friend' of yours that have bad breath, probably a story with a punch line, he'd bound to check himself out then. everyone does. good luck!