If you meet someone who is incapable of dealing with others except in a spirit of mockery, sarcasm, and derision...
Simply turn around and walk away from them. Resist the temptation to respond. Resist the temptation to reply. Above all, resist the temptation to beat them at their own game.
Just turn around and silently walk away from them. Far, far away. Remove yourself from their presence, and never return. Remove yourself. Let them be no longer a part of your world.
A full tenth or more of the Internet could be prevented if only people would follow this principle.