The Pyro Achievements are awesome, and so is the airburst of the old flamethrower.
I got the Achievement OMGWTFBBQ, and I earned it (To earn the achievement, you have to taunt someone to death. Since this taunt is a one hit kill, it's slightly easier than you may imagine). I snuck around the back of the enemy base, looking for snipers. Instead I found a spy on my own team, surveying the fight. My suspicions aroused, I snuck up on him and gave him the taunting of his life. Since it killed him, I can guarantee it was.