I launched Steam, to find this:

Quote:
We knew that Team Fortress 2 characters would be a popular choice at the Valve Halloween party (if we had remembered to schedule one, that is). We hadn't imagined that our friends, fans, and industry colleagues would have the same idea in mind. We're flattered and humbled at the intricate detail in every costume we've seen--kudos!

http://kotaku.com/gaming/halloween-hangover/

Way better costumes then the other pictures I would say.

Love the Soldier in the second picture, also the Asian doctor.

bouncing locusts...