As someone who suffered from halitosis as a child (and now has a mouthful of fillings due to the uneducated way it was handled), there are two strong possibilities that your friend might not be doing - using dental floss, and brushing his tongue.
If it's bad breath like you say, a mint is not going to help!
Also, on the subject of brushing your teeth, you might already know this but, fun fact - you're not supposed to brush your teeth within a half hour after eating. But that's not really because it will give you bad breath.