Re: Shower knives...
Four years ago, while still living in the dorms at MU (Missouri), I always kept my clothes with me in a waterproof gym bag while showering, because I didn't trust people not to steal them if I left them outisde the shower stall in that big community bathroom. In the pocket of the pants in that bag was a Victrinox multi-tool for miscellaneous odd jobs, not intended for self-defense primarily.
Really early one Saturday morning, I woke up for no apparent reason and started showering. I didn't know it yet at the time, but there was one other guy on that floor who did this as a routine to go to work, and he was always the only one up at that time.
While I was in there, heard someone come in and start doing something very quietly (I have better hearing than most). But I had no clue WHAT he was doing, since he didn't get into another shower stall and nothing flushed and none of the sink faucets started running. I just knew he was trying to be very quiet.
"If he doesn't want me to know he's here, he's up to no good," I thought. So I reached into the bag and got the knife out of the pocket, since it was the most weapon-like thing available. A moment later, I saw the shadow on the shower curtain headed right for me, so I lowered my stance a bit and started mentally preparing for the limitations of a fight is such close space (while slippery).
Then the shadow reached up, pushed the curtain aside... and turned out to be some naked girl I'd never seen before. She'd been trying to take her clothes off without being heard. She got one look at me, waiting for her, in an obvious fighting stance, with a knife, and then she ghasped, slammed the curtain back in place, and said "Oh my God, you're not Rick!"
While frantically apologizing and dressing, she got sorta babbly... Apparently, she and Rick had been talking just the night before about marriage, sex, kids, and all that stuff, and she'd decided to surprise him by sneaking up on him during one of his early Saturday morning showers when there was never anyone else around.