Peeve of the day: I send an email to one person, carbon copying two others that need to be aware of the conversation. The person on the to line is the most knowledgeable on the topic to hand. Both people on the cc line reply and silence from the person on the to line. I kind of want to smack the people on the cc line verbally noting that I was asking the other person and allowing them to 'listen'.
I am sure I am guilty of replying when I am on the cc line as well before the desired responder has had their say. I'm going to try and be more mindful of this. If I get asked why I didn't reply I can highlight my epiphany on this usage.