Here's some older ideas I've had lying around. I have more and even some basic story prompts I can share if there is an audience for them.
#1
Mom is convinced by her friends to go out dancing with them one night, later on during the week son overhears a convo between his mom and one of her friends about how she cut loose and was dancing pretty friendly with some guys. Later on son thinking nothing of it tells a couple of his buddies and unknown to him they want to fuck his mom. Son notices they seem to be around more than usual even when he's not around. One night his mom says he's going dancing and he calls his buddies but each tell him they are busy but actually set up the dance night to get with his mom and her friends. Son finds out his friends are up to something when one of his friends gf calls him later and says his friend said he would be hanging out with him at club X, same place his mom and her friends went.
#2
Son and his friends decide to celebrate college graduation by going out. Mom wants to go but son turns her down because he think it would be weird and he hates how his friends leer and hit on her. She convinces him to let her tag along and she'll pay for everything. They go to a few bars and in a half-drunken state go to a strip-club where mom gets mistaken for one of her sons friends gf by a stripper asking if they want a couples lap dance and in order to not make the situation awkward goes along.
#3
Son moves into new town and makes some new friends, they introduce him to weed and during one time while smoking at his house his mom comes home early. This is the first time his friends have seen his mom to his knowledge and one of his buddies invites mom to smoke with them. She gets high with them and son gets asked to run and get some soda. He's about to leave when he sees that his mom had already got soda and must of forgot and goes back and see his friends have started asking his mom more risque questions making it obvious they think shes hot. One friend blurts out she has great tits and the group looks on stunned while the son is hiding watching this unfold.
#4
Mom just recently had a baby a few months ago. Son has a buddy who has become fixated on his mom and son catches him one night jacking off while watching his mom breastfeed. Son's friend gets himself invited on family camping trip and sees an opportunity to break the breast pump while putting himself into a situation with the mom that would make him the breast pump all while the son watches from the shadows.
#5
Parents divorce while son is in college, he helps mom move into her new place. The next door neighboor is a 20-something year old who goes by the name "DJ Steve" and as you guess is a DJ. Son notices immediately that this guy wants him mom though shugs it off, his mom's hot and he's used to seeing that type of reaction. A couple months later son stops by his moms but she's not home. He walks in the house and sees a flyer for a rave this weekend being hosted by Steve. Again he shugs it off, just Steve trying to get into his moms pants. This is where we find out Son loves watching his mom as he goes into her room to snoop on her computer and go through her things to masturbate with. Son shocked to see his mom has recently purchased a very seductive gogo dancer girl's outfit and is planning to go to the rave! Story will chornicle what happens at the rave and after.
#6
Son is excited it's summer and can't wait for the family trip, he's even more excited then normal because his dad isn't going leaving it just him, his mom, his cousin and his aunt. His step-uncle was going up until recently when a deal fell through and caused him to not be able to go. The reason the son is so excited because he's hoping he might be able to score with his aunt or at least see her naked. He's had a huge thing for her and even made a deal with his cousin to help him get with his mom if he helps him get with his aunt. Son's excitement is soon shattered when he finds out his step-cousin is coming and bringing along a friend, the friend being a bully from middleschool that the son hates.