Here's one I've used:
Me: how do I know you're not some guy pretending to be a flaky bimbo?
Me: here's my # XXX-XXXX call or txt if you're not a man
Her: I'm not a man
Me: k, say something only a woman would say
Her: u first say something only a man would say
Me: Pull my finger!
Me: now call me
Not exactly suave & debonair, but worked for me. Modify to flow w/your convo.