I have an extra urethra. (Two holes in the head of the penis.) Until a couple of months ago, I thought this was standard male equipment, one for urine and one for semen.* This is, apparently, not the case! I have two male ancestors living, one on each side, but I’m not going to ask them if it’s my mutation or theirs.
*TMI:Close investigation reveals that one urethra is a fake and the other does double-duty like everyone else.
My brain is convinced I have twelve toes. There’s a phantom toe on each foot, between the middle and ring toes. Sometimes it itches, sometimes it aches, but there’s no possible way to scratch or rub it, 'cause it’s not there!
Oh, well now I feel like a shitheel. Sorry about that.
My ears connect up to my head at different heights, so all my sunglasses are slightly crooked.
Incomplete set of wisdom teeth (two not there at all, one is only a tiny nub, fourth one freaked out and formed a dentigerous cycst). Also one adult canine tooth never fully formed or decscended. At 48 I still have a milk tooth there.
Two hairs in the same follicle in a lot of places.
A set of wrinkles on my thumb looks like a heart with a line though it.
I can crack the joints in my feet continuously (It feels different from cracking my knuckles).
There’s something slightly wonky about the articulation of my hands, though I don’t know that it’s genetic–I’ve never noticed it in the rest of my family. When they’re relaxed, my middle and ring fingers mostly don’t touch each other; instead, each is closely paired with the other adjacent finger. Basically, their default configuration is sort of like the Vulcan salute. I tend to use them in pairs as well, like using both index and middle finger to point. I can separate them easily, and it doesn’t hamper my dexterity at all. It’s just a little odd.
I also leave four-toed footprints, but we won’t go into that.
I’ve got a benign tumor on the outside of my arm, just above my right elbow. It pokes out under my skin. It’s just a fatty tumor, but it’s noticeable. I suppose I could have it removed, but given how much I get groped by my kids during the day and night, I think I’ll wait 'til they’re a little less “handsy.”
No armpit hair.
Very convenient, I never have to wax or shave my armpits.
It is genetic; my father has little armpit hair for a man, my paternal grandmother didn’t have any armpit hair either.
Many in my family have what my cousin calls “Barney Rubble Feet.” Our second toes are shorter than our big toes. Frankly I think this is more appealing than having a longer second toe, but it does make narrow women’s shoe uncomfortable.
Also, I have the TINIEST pinky toenails on a human I’ve ever seen.
I still have two baby teeth - no permanent teeth formed there. The roots dissolved long ago, so the teeth are just kind of hanging out there. Every time I’ve seen the dentist for the past 20 years, he/she has urged me to come in just as soon as those teeth fall out.
Dude…I have that too, I likewise thought that was standard equipment. Well hell, you learn something new every day.
I have a deformed ribcage; the two sides are shaped and angled differently, with a bunch of extra cartilage growing on the one. It’s still visible, but less so the stronger my abs get. And it’s not as freaky-looking as it sounds; no one has ever noticed it unless I pointed it out. Not that my ribs have been exposed much in my life.
I have one leg 1/2" shorter than the other, which is a very large difference of that type.
I only have three wisdom teeth (my dad only had two).
I have amblyopia, which means my left eye never connected properly to my brain in infancy and continues to be myopic, weak and lazy (but I don’t have a strabismus, ie drifting ‘lazy eye’). My right eye does the extra work.
My eyes are oversensitive to light, so in normal light I have huge pupils. My pupils are also different sizes pretty regularly, for no good reason (like head trauma). Especially when I’m tired. The left, weak eye seems to slow in reaction time.
That’s all I can think of, but there are probably more. I am a very asymmetrical person.
“Colorbind” woman - actually, the technical term is “deuteranamolous trichromacy” which means I don’t see green particularly well.
My thumbs go out of joint when extended, which sometimes causes me pain when playing the clarinet or doing various other lifting/manipulating moves.
I have really long arms. I’m a little over six feet tall, but fingertip-to-fingertip on my outstretched arms measures just shy of seven feet.
I try not to drag my knuckles too much.
I have a coworker who only had three wisdom teeth. I’m at five and counting – six is lurking on the upper left, little bastard. It may or may not put in an appearance. I’m crossing my fingers it won’t, but as number 5 didn’t show up until I was about 31, I sort of think it might at some point.
Anything else I have is major, but I am jealous of your lack-of-hair from your dad, Maastricht because I got my hairy genes from mine.
I have a single eyebrow hair that would probably grow to about a foot if I didn’t trim it every now and again.
My entire left side is bigger than my right.
[ul][li]Left shoe - 9, right shoe - 8[]palms flat, my left hand is 1.5 inches longer than my right[]left breast a full cup size (or more) larger than the right[]left ear’s sticky-outtyness is about 2 cm farther[]left eyeball is larger and has the pronounced astigmatism[/li]
[/ul]
I pointed all this out to my dad, who promptly jumped up, pointed at me, and called me a freak. 
Thins thread defines MPSIMS. Moving it thither, from IMHO.