When someone has done something which causes you anger and displeasure. You respond by throwing down any item which you are currently holding and yell: "NOT COOL!". Of great importance: the item which has been throw down is now considered community property and may be taken by anyone witnessing said event.
Cool Guy: (walking into a room of friends/coworkers eating burritos) Dude, where's my burrito
Not Cool Guy: I think they forgot to make it. Or maybe I forgot to order it. (smirks)
Cool Guy: (throwing down container of guacamole
-- which he intends those in the room to now eat) NOT COOL!