My mom always said, "if you don't have anything nice to say then don't say anything" If I ignore someone it's cause I don't have anything nice to say about them.
Most of the time yes, but there are some exceptions. Like if they are being rude to you.
Excuse, what did you say? I wasn't listening.
Not if they deserve it or if they are trying to start trouble.
I'm going to pretend you didn't ask that.....