Expression used when girls posting online try to gain more attention by stating the fact that they are girls even if it has no relevance to the matter at hand.
Tits or GTFO is used in a way to say; If you are going to use your gender to gain further attention on a board or comment section of a predominantly male user base, you are basically saying "I have tits, give me more attention". Therefore you might as well go all out and show your fucking tits or get the fuck out.
Girl: Hey guys, female poster here. How do you like this video/game/whatever?
Unfazed commenter: Tits or GTFO
Tits moving in a rhythmic circular motion similar to that of a helicopter rotor when fucked. Most commonly seen in larger natural breasts it can be induced in smaller breasts provided enough force is applied. Often seen together with the ripple effect.
I was so mesmerized by your Mom's Tittycopter that I feel off your race-car bed.