Euphamism for sex. Becuz radom guys are going to come up and poke your boob and ask "Where's my bacon!?" if you wear the 'Push Button, Receive Bacon' shirt.
Random Perv: *pokes boob* "Where's mah bacon, bitch!?"\
Women wearing 'Push Button, Receive Bacon' shirt: *bitchslap* "It's being reserved for someone who's not a man-whore!"