To the femanons, no one is asking you to post tits.
'TITS OR GTFO' is a way to point out that if you're going to say your a woman for attention (because thats the only reason you would) then just skip the BS and post tits.
Most of us don't want to actually see your tits, it's just a way to get you to either commit to being an attention whore or decide that you want to commit to the discussion without using "i'm a woman" to sway opinion