joke flashback

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)