When you're just sitting there and you think of a joke and start laughing. Everyone thinks you're laughing for no reason but really you just thought of something funny. Joke flashbacks can also occur when no one is around.
Ashok: "Hahahahahahah!"
Shan: "What you laughing at?"
Ashok: "Heheh, just had a joke flashback."

or

Ashok: "Hahahahahahahahahahaha!"
(Silence ensues)
by ashack May 18, 2010
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