Define My Sister Told Me That Meaning

My Sister Told Me That
What you say at the end of an epic story, thinking that you'll will either get a laugh or agreement from your audience, only to find vacant faces.

"So after the third trip to the drinking fountain, I just didn't want anything to drink.....(vacant faces).....the end. My sister told me that."

OR

"Did you know that blind people dream?"
(Pause)
Reply: "Did your sister tell you that?"
By Gwendolin