Enemy player dominating you/your team? If you're still able to at least kill them, taunt after every kill. You may get them on tilt and cause them to do the same to you too. Anytime they get a kill off you, they'll be a free kill for your teammates.

Source : Had some trouble with a Spy main on Hightower, taunted just once after a kill, and every death afterwards almost always resulted in a killcam of him taunting in the midst of a team fight