After spending the long weekend with my in-laws who have an unnatural level of phobia about toilet seats, especially public toilet seats, I am starting to wonder: What diseases are there that you could catch from an average five minutes of skin on porcelain exposure to a public toilet seat?
It does not matter how rare or unlikely it would be to encounter it, just that it could conceiveably be contacted that way.
Depends on who’s already on it when you sit down. 
What Jill said. I’ve never understood people’s squeamishness about toilet seats. You’re sitting on it, with your arse.
You may just start multiplying phobias if you tell them this, but anything you can get from the toilet seat, you can get from the door handle. In fact, the toilet seat is probably more sanitary than the door handle. It may even be more sanitary than the air.
From Jill’s article, quoted for truth:
I really, really wish people could get the above through their thick skulls. Unless you’re making out with the toilet seat, or unless you have cuts or rashes on your butt, you’re not gonna catch anything. (Women in my office routinely spray the seat with Lysol and promptly put down one of those paper gaskets. WTF?!?)
Now get your rash-covered ass offa my lawn, and my toilet seat.
If you really want to freak yourself out:
Put some growth medium in a petri dish and cover it.
Walk into any rest room, bathroom, public toilet area ( you get the idea ) take the lid off the petri dish, leave open for about a minute then cover.
Sit back and see what amazing growths occur.
Analyse or throw up. Your choice.
I bet you could catch lice if the person right before you had a case.
No, not very likely.
Lice don’t generally live on the part of your body that contacts the toilet seat.
Who is Jill and why don’t I see her post?
Post 2 has a link to a Staff Report. The Staff Report was written by Staff writer Jill, who is also a member of the SDMB with username JillGat.
Its also best to sit down as, if you are a female, the stream may not be good and you may wet part of your undies, causing a uti or at least making the next womans butt wet.
She unfortunately doesn’t post here very often any more, though. A shame; she was one of the original staff members.
Or:
go into your own kitchen, do the same experiment and get the same result. Choose to live in the bacteria infested real world or not. Your choice.
There’s a subtle but important difference between cleanliness and hygiene.
For example, someone having anal sex concerned about cleanliness would worry about fecal matter on their dick, whereas someone concerned about hygiene might worry more about an STD.
Also, there are certain things which are transmitted mostly from our nether regions (including but not limited to arses), those regions which come into contact with toilet seats.
Are you suggesting you can get STDs from toilet seats? If so, cite? How about giving us an example of “certain things which are transmitted mostly from our nether regions”?
The doctor in the old joke said, “Yes, you can get an STD on a toilet seat, but it’s a really uncomfortable place to have sex.”
I’m suggesting that the poster who implied that it’s silly to worry about getting your arse getting dirty because it’s intrinsically dirty, is fundamentally wrong about what toilet phobic people are actually afraid of.