I don't even apologise when I'm late, I just sort of shuffle through the door and sit down. That said, I'm a couple of mins late every single day so maybe they've just accepted it. I got told off this week for sauntering in at 10 past, so I think I've found the tolerance threshold
I have some decent and believable ones prepared though, involving forgetting insulin or losing keys. Just can't be arsed wasting them if nobody is going to question me