Fuck with his mind. Put on a sexy voice in front of everybody, and hit him with the porn talk.
"You fucked me? You put your biiiggg cock in my tight pussy? You want it right now?" 5 bucks he backs down. 10 bucks he may try to rape you.

Honestly I can't help you with this. Someone is bold and there isn't much to bring him down from that, unless you want to go with the "Yeah I fucked the little dick" route.

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