I practice conversations with grocery store and other clerks, library check out clerks, etc. when I have to be out. That way, if I'm with another person in a strange situation I can occasionally figure out how to comment and be part of their conversation in some way.

If you don't want to have to comment, you could just stand and listen like you do anyway; all those times, nothing bad has happened to you, practice learning to pay attention to the conversation instead of what the inside of your head is telling you about how bad you feel, etc.?