If you're anything like me, you saw someone rocking a rad alien hat in Team Fortress 2, wondered how they acquired such a thing, then proceeded to make a sandwich and forget all about it.
Thanks to PC Gamer, I have been reminded. By earning the "Hat Trick" achievement in Alien Swarm -- beat two co-op missions online -- the sweet Parasite hat can be yours in TF2. Considering Alien Swarm is a free download, this is totally worth doing.
I'm probably the millionth person to say this, but seriously, a Half-Life Headcrab would make for a cool hat.
Get an alien parasite hat in Team Fortress 2 [PC Gamer]