I can be the boy or the girls in the following...
Maybe you are a 16yo boy. You were with your girlfriend one night. She was giving you a handjob when you asked her to suck on it. She wouldn't, so being a little pissed you asked her to lick out your ass. She freaked. The handjob came to an immediate end. She stormed off and blabbed to her friends what a sick thing you had asked her to do. Most agreed, but it caught the ear of a few bad girls. The next day one of these girls approached you and offered to eat out your butt. You were a bit pissed that your girlfriend would tell things about what was supposed to be private between the two of you. You were also surprised that some girl would actually be willing to do that. You didn't know what to say. It would be cheating. You were saved by a friend who interrupted. Then after lunch you found a note in your locker from another girl that said to wear the same jeans tomorrow that you were wearing today if you were still interested in getting your ass kissed up. Your almost nonexistent sex life was about to take a weird turn.
You have no idea how cute and desired you are by a number of girls at school. Cute enough where some are hot to munch on your ass. One of the girls might want to kiss you, suck your cock and maybe fuck you as part of the package. The other has darker things in mind. Fingerfucking you and using the strap-on that she banged other girls with to fuck the shit out of you until you squeal like a girl. Eating your own cum and wearing thongs are on the list too. Then there are the other girls who have yet to come forward.