Cut and pasted from another time this came up...
Years ago, I was out of college but dating a girl in college. She lived in an on-campus suite with five other girls. There was a big common area, three bedrooms with two beds each and two bathrooms. Two or three of them were present during my last story. It’s important to know the bathroom situation to get the full idea of how and why everything went down. The girls decided that each bathroom would belong to three of the girls and it was expected that any guests of a particular girl should use her bathroom. They did not have locks on them, for safety reasons, I presume. As you walked in, there was a sink, or maybe two on the left, a shower and shower curtain to the right and a toilet at the back, behind a public restroom style door.
Being that there were no locks, the girls devised a system to indicate if it was in use. They taped an envelope of sorts to it and put a piece of paper in the envelope, folded over so that you can see one of the four sides of the paper. One side said vacant, one said shower, potty and do not enter. Vacant and enter should be obvious but shower and potty were used to indicate that someone was using one of the facilities and you’d maybe want to announce yourself if someone was in the shower or even just wait a few minutes before someone finishes up if you’re not in dire need.
So that’s the system. I was visiting for a long weekend which I had done before and I made sure to use the system whenever I used the bathroom, but noticed that no one else seemed to use it with much regularity. I also made sure to knock even if it said vacant so as not to cause any trouble.
While the girlfriend was in class, I took a shower, making sure to put shower on the door sign. When I was done, I brushed my teeth and I did so naked, as it’s my preference to air dry a bit after a shower. If it wasn’t clear from the layout, I was facing the mirror on the left, so if someone were to walk in, they’d see me from my left side, which is exactly what happened.
I heard talking from the other side of the door, which was normal, then I heard the door open and the talking get louder. I looked to my left, with my toothbrush still in my mouth and saw Laura. People seem to like descriptions so, she was nineteen, cute, 5’4, skinny, brunette, with bigger than average boobs. She was also a virgin, and somewhat religious. Through updates from my girlfriend, I knew she had minimal experience with guys, though she had seen her boyfriends’ dick once but that’s as far as things got.
So I look to my left and see that Laura has opened the door wide open, but she's looking to her right and still talking to another suitemate. I had a second or two to make a decision and I figured that I’d be more embarrassed to be caught jumping around the bathroom trying to cover myself up than anything else that could have happened, so I just kept brushing my teeth as I looked in her direction. As she then looked forward into the bathroom, I simply said “hello.” She screamed and I swear to god jumped in the air. After she landed, she tried to slam the door closed twice, but it had one of the pneumatic pumps on them that makes sure you can’t slam it closed, so she failed in her attempts and ran away. It was fucking hilarious!
I finished brushing my teeth, got dressed and headed to “my” room, which was right next to hers. She was hiding in her roommate’s bed with her roommate. Not so much hiding, as cowering. I said hello again and with a red face she apologized profusely while insisting that she “didn’t see anything.” This was sorta kinda maybe possible given how I was standing and how my left leg was forward a bit, but I knew she was lying, which was fine. I didn’t care either way. She chilled out and she, her roommate and I decided that we’d sort of prank my girlfriend in the way she’d go about telling her what happened. I don’t even remember what we agreed on and she made a lame attempt anyway, so I won’t even bother with that. The girlfriend asked "what did you think?" before Laura got to denying she'd seen anything again.
By the time I left a few days later, we’d all laughed about it and it wasn’t a big deal. She was still sticking to not seeing anything. I called the girlfriend once I got home, hours away, to let her know I was safe and sound. She informed me that Laura told her and some of the suitemates that she did indeed see the full view but was way too embarrassed to admit it to me, which was already clear of at that point. She also confirmed to them that what my girlfriend told them about me was definitely true and that, though I was not hard, I was bigger than her boyfriend was when hard.