Gamern't - The joining of the two words "Gamer" and "not". It's used to describe someone who is not good at games.
Person 1: Broooo you're so bad at this game
Gamern't: No I swear I'm really good!
Person 1: You're such a Gamern't.
When you forget something incredibly important in a matter of seconds.
"Wait what'd you just say?"
"Oops looks like I had a john brain moment"