I once jerked off in a motel bathroom that had a fairly large window with a metal mesh screen on the exterior. It was one of those "old-timey" deals with the hand-crank to open and close the window. I was horny and feeling a bit mischievous I guess. So I decided to cum on the screen, and man did I blow a serious load on that thing! Some of it blasted through the mesh, but there were several huge, thick ropes just laying on that screen. I cranked the window closed, and went about my day. Always wondered if the maid found it. But the best part was, passers-by could easily see it from the sidewalk just a few yards from the window.
Ah, my rambunctious old days.