This happened exactly as I am telling it.
I was working in a school for a change. I had been flirting (something I do a lot) with one of the staff. We had both been sent to a stock room on the other side of the building. Actually, it was more of a disused classroom, very large with lots of dexion shelving. I made sure I brushed against him a few times, and as usual, kept up my suggestive, and lewd banter.
He had to push past me to reach something and I stuck my ass out so that he couldn't pass. Instead, I felt his hands on my hips and he pulled me hard against him. I could feel his growing hard-on through his trousers and mine! He muttered something like 'Hmmm. Makes it worth while being in here'.
I said, 'Careful where you are sticking that thing' to which he said 'I know where I would LIKE to stick it.'
Believe me, I would have fucked him up against the shelving, but instead, I undid my trousers and dropped them to the floor and told him to do it on my panties. He rubbed the top of his now fully hard dick between my legs and into the cheeks of my ass, jacking as he did so.
Then not long after he started I heard him say 'Christina, I am gona shoot.' I eased down the back of my panties so he shot his load onto my bare ass, then I pulled them up again.
Walking back to the main building I felt his cum ooze down between my legs and by the time we got there, I had to duck into a toilet and jill myself.
The next day, we went back to that stock room, and, well, isn't that kind of shelving useful!!!!