referring to a woman who has large enough breasts that aren't proportionate to her body mass and makes her to appear that she has an ass on her chest when wearing a push up bra.
Ex.: a woman who is under 5' tall, weighs under 100 lbs. and has a size D cup breasts or a woman who is over 6' tall and under 170 lbs. and has a size G cup breasts.
That little chick was fit, but with those tits; she had an ass on her chest!
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi