I trim my nails without the use of any object or mouth. I simply use my right hand nails to cut the left hand nails and vice versa. Im not sure if im making myself clear but it works. I dont know if this is a common thing since i dont go around asking people how they treat their own nails.
That's pretty much the only way I've done it for at least 15 years. I've clipped a few times but I don't personally own clippers so I had to borrow roommates. That was typically pre-job interview or trying to look extra fancy for a lady. Pretty much guarantees I always have short nails.
Like the OP I rarely drink water. I'm a little surprised nobody else is the same. Not saying I expect it to be common but figured at least a few more people would share the "habit." And for those completely unaware you're generally okay getting water from all other sources (other drinks and foods). And obviously I'm not arguing that soda and juices are all healthy for you with all the sugars and everything, just noting that someone isn't going to die because they don't actually drink much water. I can easily say I've gone weeks without drinking water straight from a cup in my past. I've tried to improve this and go some days drinking around 16-32oz of water but those are short spurts. When I workout often I drink more water so there's that.
I've put my right shoe on before my left for at least the past 16 years. I honestly don't know when it started but I remember first noticing it in middle school. My first girlfriend knew about the habit and tried to force me into putting my left on before my right because she thought it was humorous but then got really mad when I refused. Keep in mind we were twelve years old so being angry about something that dumb is more easily forgivable.
I don't like the sensation of chewing meats. Processed stuff is fine since there's little give to it and chews easily. But stuff like roasts or steak I'll cut small, chew a tiny bit, and then swallow largely whole. I'm also not crazy about the taste of steak and most meats by themselves so it all works out.
I eat kiwis whole, skin and all. I also used to eat the entire apple including the core and stem. I suck on almost all candy to make it last much longer. This was a habit formed from when I was growing up and my family was very poor so candy came infrequently and I did what I could to preserve it. My Halloween candy was stretched to last a whole year and I'd refill my supplies.
Without actually quoting...
Salsa on eggs is fantastic. I've never done ketchup. I actually got in the habit of making a can of chili, scrambling two or three eggs, and putting them together in a bowl with salsa and sour cream. It looks putrid but tastes great. Would likely be better with a thicker chili but I rarely buy it that way. I should throw in some Spanish rice...
When I essentially lived alone I showered and used the restroom without ever turning on the light. I left the door open and the place generally was lit up well and a streetlight would shine in nicely if it was in the evening. I really miss doing that.
I go back-and-forth on peeing sitting down or standing up. Over the course of my life I'm 90% standing up but I occasionally just like to sit down and relax to pee. Part of that relaxing is simply not having to think about aim or split streams surprising me or any of the other situations that could end with pee not staying completely in the toilet.
I'm sure there's plenty more and others that I'm the same as other posters and forgot about while reading through the thread.
Edit: Wow, that's a lot more text than I expected. Ugh, I often write too much.