I think what's worse is when you make plans with someone and remind them an hour before said plans begin, arrive at their house, ready to go and they haven't even dressed. Like seriously. I fucking told you I was coming to pick you up at 5, that means I will be AT YOUR HOUSE AT 5. SO YOU BETTER FUCKING BE READY. I have one friend who does this all the time, it pisses me off to no end.
I don't know about you guys, but I'm a terribly punctual person, or I at least try to be. So when I have to deal with people who aren't I get extremely frustrated. I have actually told one person whom was not ready at the time they said they were going to be ready at that I didn't have the time to hang out with them anymore, because I had made plans after them, and with their delay I was just going to move on to my later plans because I refused to wait around.