She demands you bring her something to help her through the dull party, so you sneak something special in her cup! It represents a growing, ha! Eventually I can't resist my lust for you, and I admit to you why I came here.
I beg you to fuck my tits and slide your cock between my lubed up tits.
She's embarrassed and by this point figured out the trick you pulled on her, but the growing doesn't stop! That was a good choice, as I would not have believed it if she said something to the effect that she had a small chest.