I agree that people whining at you are just being mean, but I have to say, having the toilet seat up is a real piss-off for me.

Rational reasons:

  1. Of the 4 possible (well, frequent), er... transactions that can occur involving a toilet, only one requires the seat to be up. Unless you're in a male-dominated house full of people who drink a lot of water, chances are the next person will want the seat down.
  2. Having the seat down, or better yet, the whole lid down, will prevent the beautiful aroma of excrement (or at best, stagnant cleaning fluid) that toilets can produce from spreading.
  3. It looks nicer, especially for guests. The underside of the seat tends to get cleaned less, and the rim of the toilet is often the most susceptible to staining. Much as I love to think about mysterious toilet stains while I'm washing my hands before dinner, thanks but I'll pass.

Irrational reasons:

  1. Most girls have been brought up to believe that it's just plain impolite to leave the seat up, just like leaving yer elbows on the table or chewing with your mouth open is rude. Why? Who knows. Humour us, pretty please, and we'll try not to menstruate on you.
  2. Hey, if you've lived alone or only with women for years, you're sleepy, and the lid is up, you too might not think to check to see if the seat is down. Pathetic, yes very, but probable now and then.