The veins on the back of my left hand are in the shape of the Van Halen icon.
The nail on both of my little toes grows straight up instead of forward. It’s a genetic trait that can be traced through my mother’s family.
I’m essentially immune to topical lidocaine, at least in my mouth/throat. When I was getting regular laryngoscopy, the doctor would give me a small amount of the stuff to swish around my mouth and swallow, then would leave the room to give it time to take effect. By the time he returned, what would have been for a normal person time for the numbness to kick in, mine had kicked in, peaked, and worn off.
Mine’s probably not too rare, but both of my thumbs are double-jointed, and I can “dislocate” them at will. Makes me good at thumb wrestling. My 8 year old son can do it too.
My toes aren’t particularly long but I can pick up all kinds of stuff with them. It’s kinda cool actually.
My eyelashes are dead straight and very fine on my left eye, and very thick and curly on my right, I also have oddly clicky and overly flexible thumbs and hip joints.
I can also pick up stuff with my toes, and have independent control over both little toes- I can move them both sideways and up and down without moving any of my other toes.
Not me but my son. When he was a couple of days old I finally got to hold him (he was in an incubator for the first few days) and was inspecting him. I saw that the top joint of his little finger was kinked so the finger bent out and back in again. I showed my husband, shocked and upset that a nurse had mishandled the baby. In reply my husband spread out his hands to show me that his little fingers are just the same. How could I have been married to him for ten years plus and not notice?! Both of them have kinky fingers on both hands.
I had to have eight. wisdom teeth removed.
I’m pigeon-toed. My parents were given the option to put me in leg braces when I was a child but when they heard that there are no real ill effects of being pigeon-toed, they just decided to leave it. It was really bad when I was a kid but it’s self-corrected quite a bit as I’ve grown up. The only time it’s really obvious is when I’m walking up and down stairs. The rest of the time I’m mostly normalish.
I must have freakishly short arms, because every long-sleeved shirt, sweater or jacket that I try on has sleeves that hang way past my fingertips. That’s why I love the 3/4-length sleeve trend; no more struggling with sleeves that are too long!
And I don’t think my mom took thalidomide when she carried me.
The little bump people get on their writing hand is on the right ring finger finger on me because I hold all writing utensils freakishly. When I snap my fingers I think I use the wrong finger too.
I have an assembly of sparse but rather long hairs between my breasts. And I’m not a particularly hairy person at all, so it’s really freakish.
I have curved pinky fingers. They still look slightly bent, even when they’re straightened out as far as they will go. My mother has the same thing.
I tend to get cold hands and feet, even in the summer, but not because of poor circulation. My mom and her brother both have this too, as did her mother.
I have high foot arches, sort of the opposite of flat feet. It means I get a lot of calluses on my heels and the balls of my feet, and I have to check shoes for fit in the arches.
It’s a lot harder for me to sunburn than it is for most people, and you wouldn’t think this would be so, from looking at my skin color.
My ring fingers are longer than my index fingers. This is uncommon in women, much more common in men.
I have anti-bacterial skin. When I was a lab tech student, we all pressed our hands on bacterial growth media to demonstrate how dirty hands normally are, and my media grew nothing at all. I don’t get skin infections, and my feet never smell (my exercising shoes smell like - shoes). As mutations go, it’s a pretty good one. 
Morton’s Toe, only had two wisdom teeth, hypermobile thumbs (I can “lock” them into place backwards), and my hair changes from brown to red starting from my ears and moving down.
Wow! I knew that this board was inhabited by special people, but I had NO idea of how special.
Nothing terribly severe, just annoying. Female with some male pattern hirsutism, started in my early twenties. When sandal/beach season starts I shave the tops of my toes, makes me think of hobbits.
My adult lateral incisors (eye teeth) never existed. I have a bridge with two fake teeth to fill in the gaps. The dentist seemed to think it was genetic, but we can’t find anyone else in the family with this problem. My older brother had too many teeth, so I think he stole them from me.
I have this too. I also have extremely high arches and rigid feet, so I am prone to shin splints 
I have a mole within the nipple line, so i guess it counts as a third nipple. I also have freakishly long toes and can pinch, tickle and pick things up with them. They match my extremely long fingers…
I have two teeth behind my front teeth in my upper jaw. I tell the kids I use them to bite through metal.
You might win the thread with that. So, like a shark - multiple rows of teeth?