[Welpe]

I like Rich's advice and I've used this myself at the sub-varsity level where the coaches probably aren't as experienced:

"Coach, your assistant is about to get a technical foul. That is going to cost YOU your coach's box." Provides a reminder of the incentive to keep his assistant's in line. That's probably not needed at the varsity level.

That isn't the type of comment to avoid. What you need to avoid are the ultimatums. "One more word and you're getting a T!" There's nothing wrong with being direct with a coach about how close he or his assistants are getting.

I also agree with BNR, I don't like to tell coach's how to handle their team.