I'm theoretically a guy, and don't remember ever standing to pee in a public place. I never got weird looks or anything. If I TELL people that I sit, they're very surprised and I have to make up a malformation story, but apart from that, everything is fine.
People just assume you're going to poop. Most of the time, we also pee when we do. No one would ever stand to pee THEN sit to do the rest, right?
If you're still scared, take your time. A person seeing you enter will assume that you're going to poop. If you take your time, that person will be gone, and when you come out, the people who are there won't know that you just peed.
And you can also make up a malformation story. o.o