Being late for one-off events is massively annoying and yes, I do think it's rude if you don't make the effort to calcute the correct time it will take you to get there (ESPECIALLY if you are aware that you're a late person), but people who are consitantly late for the same fucking things day in and day out? How? How can you ALWAYS be 10 minutes late for school pick up?
Both my MIL and one SIL are always late. It has taken me years to get used to it and factor it in when planning something (like a pp I don't tell my dc when their grandmother is supposed to be comng over as they may well be in bed before she actually gets here).
I arranged to meet my SIL and her dd at a national trust-type place a few weeks ago as they have a great place for kids in the gardens, it's a themed thing you walk around and get to go on various rides etc. I specifically asker her what time SHE would like to meet.
Anyway, on the way there I said to ds1 how late do you reckon your aunt will be? and we had a little bet on it. I said half and hour, he said 1 hour.
So we got there, and just as we arrived she messaged to say they were running late and would be leaving soon, so probably be about half an hour late....yeah right.
We waited, went in, did the whole walk thing, went on everything and were having lunch when she eventually turned up, almost 2 hours late.
There was a time I'd have been sitting waiting for her the whole time, fuming, with 2 very excited and restless dc. But I have learned not to take her into account any more. We'd had a lovely time. We finished lunch together and then dc and I went home because I wasn't going to do the whole thing again (dc weren't interested either).
Tbh if she was a friend I'd have dropped her by now, because really I don't have entire days or afternoons to waste hanging around waiting to do something that should only take a couple of hours. But she's family, so I arrange things which I know I can do on my own, and if she's coming round then I don't stress when she's not here as planned.
We are always on time to hers - interestingly, we turned up there on Thursday afternoon at 3pm, as invited, only to see her setting off to the shops to buy drinks......:D :D :D