Do you know about any cases of "surprise'm with a boner" that happened in the past? Would like to know who was so cheeky to do that. :-D
A few that I can think of are :
Tom Cruise removed his modesty pouch in "Far and Away" so that when Nicole Kidman's character peeked under the pot, covering Tom's unconscious characters privates, she actually got flashed. (They were married at the time so it got a lot of coverage during the press tour.)
Sharon Stone reportedly was told by Paul Verhoeven that her underwear was reflecting the light and asked her to remove it. Which of course led to that famous crotch shot which she claims was never supposed to be in the movie.
Chris Pratt whose character, Andy, on Parks and Recreation often nude and he sometimes liked to surprise his co-stars, especially Amy, by really being balls out.
Those are a few that I can remember and they got quite a bit of press. I can imagine there are plenty more where the person on the wrong end of the joke didn't find it funny and they had to hush it up.
It's amazing what just a few years can change. If Chris had pulled that stunt today, being full nude when Amy opened the door, or if Verhoeven exposed an actress without her consent then they would likely be in a lot of trouble.
That was my point. Studios are mandating modesty coverage unless it is express contractual agreed upon nudity. If a movie has any budget at all then there isn't going to be any accidental nudity making it to screen. Those are things of the past and even they are being digitally removed from new dvd/blu-ray releases of old films.