A friend of mine has a boat dealership and twice a year he hosts a big outdoor concert at the dealership. The place is big, concert is in back behind the building. My girlfriend and I did it in the back of one of the wake boats sitting on the lot. Later on she told me she lost her thong. We checked in the boat and walked the lot. Never found them.
I use to work on ATMs. It was in an ATM kiosk, in a bank parking lot, on a busy street in Houston. My girlfriend at the time came there to have lunch with me after I fixed the machine. Well, I came up with the brilliant idea....and we did 'it'!