Livre d'Or

As someone who made one of the jokes you're referring to: Yeah, that's not what I meant at all. The turnabout is specifically to flush out men who think that penetration, especially anal penetration, is demeaning, emasculating, humiliating, etc. when they want to do it to me. It's a question of, "Do you want this because you think it would be fun and mutually enjoyable, or do you want it because you want to dominate and humiliate me?"

I haven't personally pegged anyone, but it's my understanding that actually, having a prostate (which most men do, and most women don't) makes receptive anal sex way more pleasurable. So it's not actually suggesting something that should be physically uncomfortable or painful; rather it's something usually physically pleasant and frequently leading to orgasm that nevertheless requires surrendering a bit of the social definition of manhood (namely, the pride that men are Always Penetrating and Dominant, Never Receptive or Penetrated).