My ex-girlfriend and I went to the park one evening. Found a secluded spot under some trees, bushes, et.c. Started going at it...she was wearing a dress with nothing underneath, so easy access.

Anyway, a few minutes later, a dog that was being walked off leash turns up and just looked at us with his tongue hangin out.

Both of us just froze till he went away to his owner and then laughed our asses off, and carried on. Outdoors sex is brilliant, except for the mosquitos!