They probably have a self esteem or worth issue, so rise above with compassion!
Just chill because they already know you are better than them and that is why they are trying to make you feel small.
Just turn round to them and whisper in their ear that you know about their filthy habit and that you will let all your friends and work mates know about it too if he/she does not change their attitude, all will be revealed otherwise, then just walk away. It really creeps them out, I’ve done it, and it totally freaks them out. Then don’t do anything, just watch and listen. As Queen sings ” It’s a kinda Magic” you now have the power hand, use it wisely. ~ William Sneddon