Ouch!
Well, there are only two penises in our house. One of them is regularly touching me (my fiance’s) and the other once came out of my body (my son’s), so I’m not particularly squicked out at the thought that one of them may have touched the toilet seat I’m sitting on.
I do clean the toilet seats (and the whole rest of the house) after a party, but that’s just because it needs it, not because I’m horrified at the notion of touching a toilet seat that my friends’ penises may have touched.
You certainly can buy either an elongated or U shaped toilet seat at Home Depot though, and put in on your home toilet if this is a debilitating worry for you, though. I don’t, because I don’t like how the U shape cuts into my thighs if I need to spend any length of time on the crapper. So the “drawback” to making elongated or U shaped seats universal is that I’d rather buy the kind I like for my home.