Friends List With Benefits:
While playing co-op, hug 3 different people on your friends list

Overclocker:
Complete Test Chamber 10 in 70 seconds

Can’t Touch This:
Dance in front of a turret blocked by a hard light bridge in co-op

Empty Gesture:
Drop your co-op partner in goo while they are gesturing by removing the bridge under them

Four Ring Circus:
Enter 4 different portals without touching the ground in co-op.