It's a strategy in Portal 1 Speedrunning based around skipping the opening of "flippy_turret_door_12", a func_door_rotating entity, in order to save time. It is known to be the longest expression for a speedrunning trick.
Also called "flippy skippy".

code name for a gay fag

the action of shooting from a turret

When your girl sits on your dick and spins around while squirting milk from her titties that ends up in your friend's eye, when it happens, you say "69 KILLSTREAK!"