I'm not a prude, nor particularly feminist (other than the usual 'I couldn't give a fuck who you are as long as you can code' etc). But I'm still struggling to see any context where chanting 'show us your tits' isn't a completely unacceptable thing to say to another human outside of a strip bar.

And I really can't see how you can argue it's anything other than sexist, unless women start shouting 'show us your cock' at the next RMS lecture.