Tits or GTFO
Tits or GTFO, usually seen as TITS OR GTFO, is commonly used on /b/ or /s/ in response to pictures of girls that are not showing naked breasts (or nudity in general). The phrase is fairly straightforward, indicating that the girl can choose to post pictures of her bare chest or GTFO (get the fuck out).
Tits or GTFO is often posted along with an image showing a multiple choice test with two boxes labeled "Tits" and "GTFO", the text "The choice is yours" accompanying the options. The same image is sometimes posted with the "GTFO" box already checked, especially used in situations where the girl is found to be boring or unattractive.