She's turned on knowing her brother is popular with girls

Matt didn't understand women. But he'd learned one thing from watching his sister... and that was that no girl wants to be the only girl who'll go out with some guy. If the biggest jerk in the world can get a girl to go out with him, all of a sudden, other girls will want to as well. What he didn't know was how his sister would react to a nude selfie from Cindi.

"Looks like you have a choice," Karen said. "You can jerk off looking at this picture of your girlfriend, or you can teach me how to give a good blowjob."

"You're kidding, right?"

"I've got your dick in my hand," Karen said. "Do I look like I'm kidding?"