I think the real dick move was that the guy finally got you to trust him to take the bike out and "keep it under 20", then he guns it. What an ass. You're lucky he had the money to hand you and you shouldn't feel bad about taking/using it. I would NEVER let anyone take my bike out, unless I absolutely trusted the person 100%. If somebody wants to try a bike that badly, they can get their own. With the money he handed you he could have bought and wrecked his own bike instead of yours. Just my two cents and yes I'm a little bit of a selfish bitch sometimes.