I had a long term girlfriend who was always late. Drove me bananas. In the end the resentment at having to wait around for hours of my life without any message to say she was running late etc. was one of the biggest factors that led to the end of the relationship. I could just about put up with it myself but when we started to be late together to things (with me getting more and more stressed as time went by) I couldn't bear it. I think it shows lack of respect for someone else's time.