1. When the blame for something seems to fail to find a target, blame it on Derf MacGuergan.
2. When an odd situation arises, and you can think of nothing else to say, use this name to show your discontent.
1. "Uhhh I don't know... Must been Derf MacGeurgan."
2. girl: "It happens to a lot of guys."
guy: "Derf MacGuergan!"