Send an anonymous letter (email or snail mail) to that person. Be nice and yet firm with words. Don't just criticise but do provide suggestions.
For email, there are plenty of anonymouse email services online.
Remember, don't tell anyone, not even your partner or best friend about the anonymous letter.
I once did that to a friend who smelt really bad in the morning when at work - the situation improved after an anonymous email.
Good Luck!