Oh boy, nasty can of worms you guys opened. Just off the top of my head I can list a few places that might be considered weird.
In the movie theatre during a bad movie.
In the last subway of the evening.
On an empty bus. The driver was straining hard to see if we were doing anything at the back of the bus.
Boiler room of my high school. Actually everywhere in my high school. The janitor caught us so many times that after a while he would tell us to lock up on the way out.
Stircase of a Hospital.
Elevator. Any elevator was good. We let it run and stop our activity when the elevator stopped. I used to love eating out my GF in the elevator. (skirt, no panty)
Top floor of MANY office buildings.
My balcony where my girl was bent over the rail fully clothed with her skirt hiked up from behind where everybody could see. THAT WAS HOT!
Hanging halfway out my dorm window.
Top of a bunk bed with the other room mate drunk and sleeping on the bottom.
Club stairway.
In the back seat of a car while my friend is driving.
My toe in my GF's pussy in an upscale restaurant. I made her take off her panties in the car before we went in. She came so hard that I thought we would get kicked out.
Blowjob sitting in the Economy seat of a plane when most of the people were sleeping. I had a blanket over my GF's head.
In rush hour I ate out my girlfriend (I was driving) with 4 fingers inside while she kept an eye on the traffic to see if it started moving again.
In MY ass. (a twist to the NewlyWed game but true)
The best one was when I broke into a gym in the middle of the night because this girl had a thing for the smell of sweat. We did it in the change room. The showers were very convenient and we left the gym early in the morning just before they opened. Maybe it was the fact that I just did a B&E but it was a really hot evening.