Other people doing a lot PDA makes me uncomfortable. You know, people where you want "GET A ROOM!!"
Holding hands, hugging, and kisses on the cheek are ok with me. Pecks on the lips are ok sometimes but anything further than that I am not really in front of people in public places.
It's also different when you're in a same-sex relationship because you're worried about how people view it, moreso depending on the area you live in.
Like negative or rude comments being made to you. Or not being "out" to everyone in the community. Or if you live in a very conservative and heavily redneck populated (I am not insulting the nice rednecks, just the stereotypical ones) area, some people are worried about safety.