Why some adult people arrive late and are horrible with time management?

Yesterday my cousin wanted to come over at my place since she couldn't finish unpacking so she ask me that she was going to stop at my house to eat lunch without asking me first in advance I scheduled plans ahead of time. My cousin straight up told me I will be there at 12:45 pm I was annoyed I was doing my Spring cleaning ok so I stopped what I was doing and went down stairs to the kitchen to cook lunch. Now this is what bothers me long story short my cousin arrives at my house at 1:30 so disrespectful and inconsiderate. One thing that infuriates me is when people arrive late no phone call nothing. My cousin told me she would be at my house at 12:45 pm people have things to do and this unacceptable. I had to be somewhere at 2 p. m. to pick up an order I had place for an outdoor table my cousin is over her thinking she is the daughter of the president as if she was that special šŸ˜”šŸ™„so disrespectful. My question not all people but why some people are so disrespectful and arrive late just horrible just horrible time management. Yet my cousin called me a Karen when I comforted her of her grandchildren inconsideration and disrespect. When I set up times with people in general I arrive 15 minutes early. I just can not understand inconsiderate people.

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I meant to say *Inresponsible behavior not grandchildren
Why some adult people arrive late and are horrible with time management?
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