If these guys weren’t blinded by the opportunity to possibly spend some naked time with a woman, they’d probably pick up that Michael’s trolling them from the start. But they really never do seem to learn.
The challenge to “hot dog boy” is simple: put some mustard on your nipples and send him a photo of it. And if they do that then they’ll know you’re for real.
The thing is, the guy seems to know what’s going to happen to him: whoever’s on the other end will screenshot it and turn him into a meme.
So of course he’s not going to do that, which is why he offered him a compromise: put the mustard on his face instead.