I've never quite understood the big deal about men leaving the toilet seat up but since I hear so much about it I try to comply.
I do have a pet peeve. Sometimes when I lift the seat there are obvious signs on the underside that a female has used it and not bothered to 'tidy up'. I never hear this broach of etiqette mentioned. Yecch, makes me sorry I touched the damn thing at all and I sure don't feel like touching it again to put it down.