One thing that pisses me off is when I'm sitting with my family in church, and 30 minutes into the mass, a 12,000 member family walks over, and instead of sitting in the 5-6 completley empty pews near us, they choose to site in our pew. First, if you're going to be 30 minutes late to mass, don't come at all, and second, there are 10 empty pews around us. USE THEM.
My parents visited a Church for Mass once while on vacation. They sat in a random row in the back of the Church. In walks an old woman. She stood there, beside the pew, silent, and waited until my parents got up and moved to a different pew. She didn't even look at them... just stood there in the aisle and waited. I guess they sat in the same seat she's been in for years.