Glory hole surprise.
The small city my wife and I live in has three adult toy shops. I frequently stop into one of them on my lunch break from work, as it is only two blocks away from the place I work at. If I ever get caught going in or out of the place, I just say that I was checking out toys to buy for my wife. The truth of the matter is that they have a private/secret glory hole set up down in the basement where you can go and get your cock sucked or fucked by an anonymous woman through a small hole in the wall. My wife is generally at home several miles away during my lunch break, so there is very little chance she could ever catch me going in there.
So anyway, on my sons 18th birthday, I decided I would take him into the porn shop and treat him to his first blow job and some pussy. My son was always a shy kid who doesn't have any friends and has never had a girlfriend, so I knew he would enjoy it. I told him to meet me at work during my lunch break, so I could give him his birthday surprise. I asked my wife if she could drop him off at my office, but she said she had plans with a friend and couldn't do it, so I gave him six bucks for a cab to my office.
He showed up right on time, and asked where his surprise was. I told him to follow me, and I led him down the street to the porn shop. His eyes lit up as I led him through the door. He said he had heard stories about the place, and I told him what he had heard was likely true, and that he had to promise not to tell his mother about what we were going to do. He promised, and I took him down to the basement to the glory hole room. I showed him the two holes in the wall and explained that one hole is for getting a blow job and the other is to fuck some pussy. He said he wanted to start off with a blow job and finish with some pussy, so I told him to get undressed and stick his cock in the first hole. I left the small room and waited outside the door for my son to finish. I could hear him moaning and having a good time, and after about five minutes I could hear that he had cum. He got dressed and came out of the room with the biggest smile I had ever seen on his face. He gave me a big hug and thanked me, then I told him to head upstairs and wait for me while I payed the lady behind the wall for her services. I knocked on the door behind the wall and asked her how much I owed her. She said $50 and opened the door up to take her money. I'm not sure who was more surprised, me or her, when I saw my half naked wife standing in front of me, with our sons cum dripping out of her cunt.