Keep my seat warm

Have you ever sat down in a public area, such as a bus or bench, right after somebody else was sitting there and it's still warm? I don't know about you but if you have had this happen, it actually grosses me out and I can't exactly explain why. It's like a reminder of somebody else's germs or body are left behind. It's weird, but I think about it every day on my bus ride home. I have had this happen so many times now and every time I wonder why people say, "keep my seat warm" when they get up, maybe it's a way of asking somebody to save their seat, or maybe they don't care if it's somebody they know. But for the most part, after sitting in a few people's warmed seats, it's unlikely that I will be using that phrase again.