The phrase TMI bothers me. One way it bothers me is entirely personal and revolves around my lack of a filter. I don't mind people talking about topics that are normally banned from polite conversation - if someone wants to talk about how recently it has hurt when they pee, describe in great detail how and with who they had freaky sex last night, or go on about the mould they had to clean out of their fridge, I am quite happy to listen. TMI irritates me because it is often used to shush people on the basis that certain topics are deemed unacceptable for no good reason. I don't mind if a person doesn't want to hear about a particular thing, but it bugs the hell out of me when they assume that I have some kind of obligation to never discuss such topics because it is *wrong*. "I don't like that" and "that is morally wrong" are really different.
The second thing that bothers me about TMI is when it is used as an excuse for bias and bigotry. Gay people are used to this; people will say that they don't mind someone being gay but having to see two gay people kiss is just yucky and TMI. It is often accompanied with the phrase "don't shove it in my face", just to make it clear that the speaker feels entitled to supervise other people's displays of affection. Of course this isn't applied when it is straight people doing the same thing, and that is the problem. If someone doesn't like seeing displays of affection of any sort I will snort derisively but I accept it... but when their dislike exclusively appears when the people in question are gay it makes my blood boil. Just admit you are bigoted against gay people and stop pretending they have some social obligation to hide themselves, okay?
I see this a lot with attitudes towards polyamory. A letter to Dan Savage this week was on this topic: The writer is polyamorous and ended up inviting a person they were dating and a person that person was dating to a party with mostly monogamous 'normal' types. One of the monogamous people felt obligated to leave, unable to cope. Some of the commenters defended that behaviour, saying that being open about being polyamorous is offensive, likening it to telling everyone about the gigantic crap you had just finished dropping. After all, this theory says, nobody wants to know about who you are sexing, that is just TMI.
That attitude is bullshit. It isn't like talking about taking a dump, it is like a bunch of white people gleefully talking about all the dumps they have taken, and when a black person speaks up about their dump everyone telling them they are being disgusting and they should keep it to themselves. Everyone would agree that such a situation is clearly based on bigotry, not poop, and the poly situation is the same. Nobody would balk at "Hi, welcome to my party, this is my husband Steve." Why should they feel entitled to be offended when the introduction is "Hi, welcome to my party, this is my husband Steve and my girlfriend Anisha." It is the same damn thing, and anyone who suddenly claims TMI and righteous offence in such a situation is just unwilling to own their bigotry.
Maybe there are people out there who cry TMI when they see a wedding announcement, a picture of a newborn, or a celebration of an anniversary from someone in a straight, monogamous relationship. Those people (all two of them) are totally entitled to be grossed out by someone mentioning that they have two boyfriends, or that their kid is being raised by three adults as a unit. Those two people are weird, but at least they are consistent. Everybody else who treats the first set of cases as totally normal and worthy of a smile needs to learn to treat the second set of cases the same way.
Or, you know, just say "I am highly biased against non monogamous relationships" which is at least honest, though not exactly without reproach. In the same way that gay people don't expect straight people to switch teams, poly people don't expect mono people to suddenly start dating everybody at once. Do as you will, just don't pretend that other people publicly being different from you is some kind of violation of your rights.