Under any circumstances. Just don't go there. They are not worth your time. If they are in the gray, let them stay that way. Do not give them attention. Do not draw attention to them and their responses. Responding to them not only wastes your time and gets you needlessly riled up, it also un-grays them and opens the door for more.
Not cool, bro. Not. Cool.
If they are assholes, dismiss them. If they continue to be assholes, alert a mod. Otherwise, let it be.