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When someone forgets there Jam (favorite song).
Danny: You forgot your own Jam?
Brian: I had Jamnesia
by vobman August 29, 2015
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In the sport of roller derby, at the end of a jam, when a player skates back to the bench and can't remember a single thing that just happened on the track. Caused by a combination of nerves, adrenaline, overload of quick, in-the-moment decision-making and whatever you call that thing your brain does where it represses things that are painful.
"WTF just happened out there? I have wicked jamnesia! Who got lead jammer? Why is our jammer in the box? Did I do anything good? Who was my partner? HEELLPPP!?"
by KittyT February 25, 2011
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When you forget what you jam is called.
Partyguy #1: What's my jam called again. Oh yeah, Fantasy that shit's my JAM!1

Partyguy #2: You forgot your jam?

Partyguy# 1: I have jamnesia.
by Morgan Freeman's evil Piñata. September 16, 2015
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