I don't know if this one has been brought up before, but I was reminded how much I hate the phrase below when I read it today on the forum when a newbie poster was attacking another forum member.
"No offense, but..."
When I see that, I know your meaning is, "I entirely intend to offend you and tell you how much you suck, but I'm trying to cover my meanness and unkind thoughts with the thinnest veneer of civility that everyone can see through."