Have you seen your parents kiss each other?

Yeah at their anniversary dinner - let's say, it is one anniversary I won't forget for the rest of my life. -_-'

Never.

Every now and then and it grosses me out.

Light kisses, yes.
Making out or passionate kisses, no.

Yeah. I've seen them give each other a peck on the cheek, and lips; and make out heavily. When I was younger, I walked in on my mom giving my dad a blowjob... heard them having sex many times, and saw them having sex outside once when they thought they were alone.
Parents kiss, and have sex, more than we may think. It is actually a beautiful thing. I really don't know why so many people aren't comfortable with it, and don't understand that it is healthy and normal.

My parents were married till I was 7 and I don't remember ever seeing them being affectionate. But neither one of them are affectionate people in general so.

They would make out passionately like a couple of love birds. Especially when my Dad got home from work.