Whether it's your friends or parents having non cheating sex with each other, what would you do if you opened that door and saw them doing the dirty deed?
Personally, I wouldn't know as my mind would blank out and I'd only figure out my reaction afterwards. Oh, well... at least I got a glimpse at how I got concieved...
But it's not something you want to see at fifteen years of age.
Immediately shut my eyes, walk out and close the door behind me. Then proceed to leave and act natural the next time I see them. Shit happens, I don't need to add to the trauma by losing my shit.
My scenarios...
1 Girl, 1 Guy - Tell him "Is it my turn yet?" (Awkwardly walk away)
2 Girls - Ask them "Room for 1 more?" (Then slowly lock the door behind me)
2 Guys - Yell "How DAFUQ you get here?" (Then awkwardly walk away)
Hmmm....I've walked in on parents before and all I could think of was...Yes!!! not because I wasn't traumatized but because my you know *wink*, was far bigger than my dads and it changed the status of "Man" of the house....but I also didn't sleep for two days...o_O
Doesn't matter who so much as where, for me. If it were in my room I'd be like "Get the fuck out."; if I walked in to someone elses room I'd just walk out, or if it was a public place I'd act as if nothing was happening.