He's suspicious

"Okay, nice try, Alex." Ryan scoffs and smirks at you. "This is a prank of some sort, right? Did you plan this with Sophia? Are you filming me right now?" He looks around as if trying to find a camera. You reassure him, "No, no prank. I just... really need to get fucked and you're a good friend so I thought you'd help me out. What's the big deal?"

Ryan rolls his eyes. "Oh suuuure. We've been friends for years now, and you're suddenly so incredible attracted to me that you came here to have sex. You expect me to fall for that? I know I'm dumb, but come on..." You're taken aback by his response, but thinking it over, it makes perfect sense. Neither of you have shown any interest before, why would you come out of the blue and ask for this now? It's not that Ryan isn't attractive. He has cute messy blonde hair and keeps in pretty decent shape, but you've always just seen each other as good friends.

How on earth can you convince him you're sincere?