Tell him no way

"Look I didn't suck your cock because I wanted to, I just did it to prove I wasn't a cop, I'm not into guys."

"Well I admit you didn't know how to suck a cock, but you didn't put up a fight at all just pulled my cock out and started to suck on it. I would have let you suck it longer but I was in a hurry to get out of there. However I'm not a bad guy we can come to a deal, one blowjob for one line of coke, which means you owe me a blowjob and it's time to pay."