When I was a senior in high school I was on the varsity baseball team, and for some reason a couple of our games were postponed and one of them had to be made up after our graduation. It was an afternoon game and after it was over and we had our showers, a few of us decided to just wander around the school one more time. The only people that would have been there were a few janitors, but they didn't start for a couple more hours so there really wasn't anyone around that would give us a hard time.
We walked around for a little while looking through the windows and talking about the past four years, when the idea jumped into one of our minds that we should leave some kind of mark. We tossed around ideas of leaving messages on the chalkboards, rearranging things in the rooms or TPing the lockers. We kept walking around not being able to decide when someone said we could jerk off in one of the rooms, leaving a nice 'mark'. Everyone got quiet and he said he was just joking around, but a couple of us said it wasn't a bad idea. The longer we talked about it the better it sounded, and we decided that's what we should do. We had to figure out where to go and we decided to use the teacher's room that we all couldn't stand. The doors all had locks, but they were simple ones you could open with a quarter or something flat so no one could lock themselves in. We popped it open and walked in, leaving the light off just in case. Class had been out for a few days before the game, so we knew the rooms were already cleaned and wouldn't be checked for the next few months.
We all sat down in the desks and talked about things that would get us horny, and pretty soon we were all getting hard-ons. A couple of us just slipped off our shorts and sandals but the other two decided to get completely naked, so we followed suit. The next 15 minutes were quiet except for the sounds of our hands slapping or the occasional grunt. When the first one of us was getting close to cumming he asked where to shoot it, and someone said to blow it all over his desk. He stood up and stroked faster, and when he came he shot three thick loads of cum all over the desk. Watching him finish set the rest of us off, leaving our cum all over the place. I was the last one but I decided to do something different so I hurried over to the teacher's desk, got up on my tiptoes and came all over it. We laughed about what we just did and sat around in the room for a while, just talking and bullshitting. I was sitting in her chair with my feet on the desk still naked and I started to get horny again. I started stroking again while we talked, blowing a second, smaller load on the floor.
We started getting dressed to leave, but one of them decided to stay naked, so he was walking with us with his cock rock hard again and bobbing back and forth. We almost got to the door to go outside when he said to hang on for a second, stopped and started stroking for about 10 seconds before cumming again. He milked out the last few drops before putting his gym clothes back on and we walked out to our cars.
The next day we got together and we couldn't believe what we did, but it did give us a memory and something that probably hadn't been done before.