I'm a social worker, so this happens all the time as a job hazard. When they bring up health crap, I jump in quickly with much concern in my voice, tell them I have no medical knowledge, and ask if they're seeing a doctor and getting it taken care of. If they say yes, I end their train of thought by telling them how relieved I am that it's being handled, and quickly change subject. For other topics they seem to need to vent about, I focus on my breathing and meditate a bit so as not to get sucked in, then find a way to jump in and refocus when I can.

Try looking them in the face and saying "I'm really sorry to interupt but I'm having a really heavy period, my head aches, my piles are playing me up giving me a massive pain in the arse and so I can't really pay attention to your inane twaddle, so excuse me while I go change my jam rag"
Smile sweetly and walk away.

All i can think of now is ...."one time at band camp ....."

I try to hold back but people have been so supportive here. Why we have Groups. I created a cancer group for those who need support, need to vent and bear their souls.

Difficult - I generally make faces when the details start to get too personal, then at the first opportunity I say something like - "Didn't need to know that." or " TMI Dude, TMI."
It will depend on, of course, who it is that's sharing, but some appropriately phrase of "Too Much" along with some awkward and uneasy looks has done the trick for me.
Later - if that person resurfaces, I cut to it and before they start chatting, and ask if we have to talk about "the personal topic" again... That typically dissuades them from bringing it up.

I cover my ears and go "la la la la la" until they stop

I look for ways to bail from the conversation.

A specific phrase, such as "too much info," along with an obvious hand sign of some sort, usually work for me; with a bit of repetition, you could cut it down to just the hand sign after a while.

Good luck with your unsolicited imbroglio!

I don't usually get uncomfortable if someone shares personal information with me. I take it as a sign that there is something about me that makes them feel comfortable to open up. It's a compliment.

I just tell them I don't want to know, zero interest. Yay autism wins again.

I am extremely comfortable with myself, but I kinda cringe when I get unwanted info from others; usually I just move past the comments as if I didn't notice them

A person who tells the good and bad about themselves is opening themselves to the world, saying here I am, warts and beauty marks. The must be confident and capable of accepting criticism for the warts, without sweating it.

Things that occur in one's life make us the way we are. Knowing those things helps others understand why a person does something. A few hundred years ago, when few people traveled more than 20 miles, everyone knew everyone in great detail. In this world, if we are to make good friends, we must tell them. Being secretive can impede that process, or prevent friendship.

Why do you want to keep secrets.

I just figure they really needed to share that and I am glad to have been able to help them. we all have our own crosses to bear.

Just start acting way too interested by whatever they're saying. ?

At some point I let it go in one ear and right out the other. That way you don't upset the person speaking to you.

I don't know since I probably am the one that is guilty of it. Though, I have gotten better about it. Usually my anecdotes have a humorous ending. Nonetheless, I have had people share details that went far beyond even my moderate openness, and though I don't think this is by any means the best way to handle it, I usually just sit there quietly and hope they stop sharing or try desperately to change the subject.

in australia, where women have to keep their breasts covered during a check for skin cancer, people don't "go there".

I have this state of ignoring and paying attention at the same time it usually is followed by a remark, oh yea or that is nice and sometimes even a head nod for added effect.

It depends on who it is tbh. If it's my little SIL just know if you tell her anything best to stick to something you have for sale so you can save money placing an ad in the local newspaper, because news will travel far and wide no matter who you are!

I kind of figure whoever it is is going through something and try to be compassionate as I've had my own tmi moments, probably on here even. Just nod and say "oh wow that sucks", or "that's awful" etc etc. YMMV

I pretend to listen but my mind is some where else

It depends. I find "Do you mind? I'm eating." or "I'm glad you told me that when I wasn't eating" cover most of the bases.

I'm too curious, or just plain nosy, for this to be much of a problem for me. Some stories I would rather not hear such as confessions of sadistic cruelty. I give those people lots of warning not to proceed. If they continue, I can be quite rude before I leave the scene.

Do you know Jenny? She's my coworker, who goes into awkward detail about her life, all of her relatives' lives, and her husband's erectile dysfunction.

Okay, in my case I have to workwith this woman, so I listened, offered no advice or support, and tried to erase the details from my memory. I had to just cut out of when it got to the point where she texted me in the middle of the night because her tattoo artist threatened her with a restraining order for stalking and she wanted an alibi, because she WAS stalking him.

I'm not sure what to suggest in your case. Do you know the motive behind their oversharing? Have you told this person that you're not comfortable? Can you just avoid said person? It's not me is it?

I let my mind wander...