This would definitely drive me crazy. I have a couple of American friends who are like this and it's really hard for me to not get angry when they are 45 minutes late to something.

I honestly do not give a shit what time someone shows up to a social function as long as they say an accurate time.

If you want to meet at 8, then lets meet at 8, but if you say 8 and then don't show up til 9, what the hell.