Lateness is just plain rude. It is about valuing their time over yours, of course their are genuine reasons occasionally but the majority of late people just don't care about keeping you waiting.
I am really disorganised, like naturally I am a total mess. I have to work really hard to be on time. But I still am on time. I just have to factor in random extra time for all the faffing I know I'll do.
If you know you are ways late why don't you just plan to be early? For example if I know I need to leave at 12, I plan to be ready for 11.45 and then will just sit and relax for 5 minutes before I leave. I will wait in my car for 5mins/grab a coffee whatever, so that I am there a bit early and know I will make it on time.
I have the philosophy on time is 10 minutes early, so if you have to be somewhere at 11, aim to be there for 10 to. Then you can just relax in your car or the cafe whatever the scenario for 10 minutes.
Because really that's what it comes down to, you can never plan exactly how long something is going to take. So someone will be waiting around a bit, the people who are always late make sure it's just never them.
To the people who say "I always end up doing something before I leave" why don't you just not do whatever it is? Like you know you are always late, so you do know you don't have time to do it because you are always late. Yet you do it anyway.
Or "I always forget about the little things". Again you know you are always late, you don't have to remember all the little things. You just have to recognise that you are always says 20 minutes late so aim to leave 20minutes earlier. Everytime. You do know you have to do these things because you are always 20minutes late, you know it's going to take you longer than you think so you need to factor that in.
If you know you are late/have poor time keeping whatever then you need to factor in a lot more time in your leaving process. You don't need to allocate it to anything, just give yourself longer. Because even if time keeping is poor, logically your not always going to be late, your timing will be all over the place. If you are always late then that means you just haven't given yourself enough time.
Time keeping really doesn't come easy to me and that's why I get even more pissed off when someone's late, because I have gone to a fair amount of effort to be there on time. I haven't done whatever it is then were doing that made them late, ill still have to do the washing up/laundry whatever when i get home, I have just been sat waiting for them. It's waisting my time so that they can get done what they wanted.