8b609377_Atlas_gestures___Portal_Wiki__How_To_Unlock
[Name] Team Tease [Description] Can only be performed when Atlas is near P-body. In this gesture, Atlas takes the head part of P-body and places it on the ground while laughing. P-body will take his head back and smack Atlas with it. [How To Unlock] 
Complete the Mass and Velocity Course.
Atlas gestures - Portal Wiki
How To Unlock