forWhen I opened the envelope I found a cheque for/of $100.
toWhy are you rude with him? Can't you be nice to/with him?
Say: "Why are you rude to him? Why can't you be nice to him?"
I would say about. Generally, we express disappointment with (or in) a person.I'm disappointed with/ about the hotel.
We weren't very impressed with/by his appearence.
forI felt sorry about/for the children. They couln't go to the party.
If there's a rule, Cas knows it.
[Edited to change something.]