Taunts

From TF2 Wiki

Each class has its own series of taunts. These can be performed at any time (Default key: G for PC, "X" for Xbox 360 and "Square" for PS3), with each class having a separate taunt animation for each weapon. Each taunt has several lines of dialog that are chosen at semi-random (one taunt is chosen at random and every taunt after it follows a specific list). Taunts are generally used to challenge or insult a player on the enemy team. Exercise caution when taunting. You are vulnerable while performing a taunt as your view will shift to third-person and you will be unable to act until the taunt is concluded. Some weapons do not have taunts, such as the Electro sapper. No taunt causes damage, not even the fire produced from the Pyro's Hadouken.