I believe the appropriate response to a misquoting of that particular line is:

Raising a finger: “Um, actually…The real quote is…”

Raises fist and in a deep voice: “If you only knew the POWER of the Dark Side…Obi-Wan never told you what happened to your father.”

Replying to yourself in a not-so-deep voice: “He told me enough…He told me you killed him!”

Back to the deep voice: “No…I…am your father!”

Then in a pained and pitiful voice: “No…no…That’s not true…That’s IMPOSSIBLE!”

Now with the deep voice again: “Search your feelings. You know it to be true.”

Lastly, with a whiny, agonized scream: “NOOOOO!..NOOOOOO!!!”

Then just stand there smugly, letting them bask in your infinite knowledge.