Pet pieves

I just thought of a couple of things that really annoy me. The first one is when you say "Thank You" to someone and they respond with an dull "OK". OK? wtf does that mean? Sounds like they don't care for your gesture. Another one that bugs me is when you hold the door for someone and as they walk through they also have to hold the door, as if I am going to smash it in to them.