The former is a figure of speech used before a (generally mild) complaint or observation. The latter is a term (also seen on TVTropes) to describe a classic moment of hilariousness in a movie or TV show that stands out above all others.
Jude Law: "Call me old-fashioned, but one doesn't have sex with women who are unconscious."
Scrote: "UR GR8, M8!"
Grown up: "Call me old-fashioned, but I make it a rule to ignore words with numbers in them."
Venkman: "Mother pussbucket! Nobody steps on a church in my town!"
Ted Striker: "I flew single engine fighters in the Air Force, but this plane has four engines. It's an entirely different kind of flying, altogether."
All (together): "It's an entirely different kind of flying."