This is a person who has recently given up smoking
and automatically considers themself to be the voice of morality
that must preach unto any "unclean" smoker they come across.
It usually starts with the snide comment, muttered under their breath: "Dirty, filthy habit that.", soon followed by: "It'll kill ya".
These are the kind of people who I would like to throw down a hole with a pack of angry pit-bulls and make them fight over a lump of meat.