"Be Kind" - are the two words I use a lot with our grandson. 2-1/2 years old, but can be quite aggressive at times. Instead of constantly saying "No" or "Don't", I say "Be Kind", and he immediately stops whatever he's doing (usually to his big sister). Those words seem to have a distinct impact on him. I wouldn't hesitate to use them on an adult.

It's true, JJ, so many people are struggling with their own fears, insecurities, situations, losses, angers...it leaks out through a myriad of behaviours, including rudeness.
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When you don't like a thing, change it.
If you can't change it, change the way you think about it.

(Maya Angelou)