This happened to me one week ago on the date of 11/19/12.
I was told constantly by my mom to take out the garbage and then take a shower, but I kept ignoring her. After her constantly repeating herself, I decided to get off my butt and take out the garbage, and walk towards the bathroom to take a shower.
I was in the bathroom, and decided to get rid of my clothes and start the water. I was cold, so I decided to take a warm shower. I turned the temperature nozzle to high and waited for the water to warm up before entering. I was in there for only a minute, adjusting the gauge to cool the temperature a little.
I noticed a sound that was like a curtain being opened. I turned around, and in fact, the shower curtain was partly opened. I thought I probably just forgot to close it entirely, so I just closed it. As soon as it was closed, the water began to slowly cool.
I decided to see if turning the temperature gauge higher would help, but it seemed to do nothing. I heard that sound again, and not only was the curtain open, but a man with closed eyes, pale skin, and a bald and wrinkly face was looking at me with a very creepy and large frown.
I was scared frozen in place for about 5 seconds. I panicked and decided to run, after punching him in his face. He fell back, but he got up instantly, and ran towards the door and down the hall.
I got my towel and ran towards the direction he went, and as soon as I turned, I saw him leave through my front door. I looked through the door and saw nothing. I ran to my bedroom, noticing the shower was off as I passed and grabbed the first clothes I saw, before running back to the living room.
I heard a voice, but I realized it was just my parents. They asked me why my door was opened. I told them I went to take out the garbage and forgot to close the door. They got angry at me and started yelling at me for about thirty seconds. I went to sleep and actually had a pretty nice dream, despite the fear I had in my bed.
I continued the rest of the day, but had to take another shower the next day. I told myself not to be afraid and take a short shower. After two minutes, I turned it off, got dressed and went to the living room, relieved nothing happened. I had taken 3 baths since then, and never had the same incident again.