A few years ago, I spent two hours reading internet webpages about how to be more punctual. I've struggled with being non-punctual throughout my life, and it's always one of my New Year's Resolutions.
One page talked about how if you are trying to get your late friend to improve, it is not productive to say "You are late again! You're always late! Why are you perpetually late! You are just a late inconsiderate person!" That reaffirms in their head that part of their self-identity involves being late. You've said they're selfish, and they'll sink to your expectations.
Instead the web page suggested you say, "You're late -- how unlike you." Then the person will want to rise up to the expectation that they're characteristically punctual.
I realized as soon as I read the words that this would totally work on me.
If it is too disingenuous to imply that they're punctual, you could use a variant such as "You're late -- how unlike you, since you're usually so thoughtful about everyone".
When I lived in my Mountain View townhouse, I threw parties every year or so. After the second one, both of my neighbors complained. One wrote me an angry note that said, "You threw a loud party again! This is unacceptable! We complained last year, and you did it again!"
The other said, "I know you're a considerate person, so I want to let you know that the noise from your party disrupted several of us. Thanks -- you've been a good neighbor."
Which one do you think made me feel sheepish and determined to go the extra mile to make absolutely sure it never happened again?