i like the revenge idea. but we all know that the bra isn't gonna make her jealous. if you want to make a woman feel inadequate as much as she has made you feel inadequate about your penis, you have to go after her weight. that's the only thing that will get into a woman's head as much as penis size comments will get into a man's. women get over the self consciousness about having small breasts pretty quickly. if they didn't, there'd be a sbsg.org, and there isn't. BBW is a pretty common internet term though, which has roots in self consciousness just like SPH does.
so, yeah, you can battle magnums with... oh, i dunno... maybe she finds a picture of a reeeally thin, athletic girl in your drawer by accident some time, or gets a bottle of diet pills as a surprise present...
unless she's already really skinny. if that's the case, then take your hand off the mouse, back away from the keyboard, stand the fuck up and run for your life, my man. cuz you're about to embark on a self consciousness journey which will ruin your relationships and fuck with your head for possibly the rest of your life.