Rusty Brain 

A sex act, similar to the rusty scupper, where a man and woman are engaging in anal sex because she is having her period. Shortly before climax, she pulls out a strap-on and rubs it all over his face. She then yells "Welcome to the Thunderdome Bitch".

Much to his eventual dismay, Lisa pulled a rusty brain on her boyfriend while she was having her period.

Rusty Brain by Brucestafer August 3, 2008

brain rust 

A term given to someone who doesn’t use so it goes unused/rusty.

This is used as an insult, basically calling someone dumb. Often used for people who value feelings and opinions over logic and reality.

Person 1 - “Does this novel have pictures in it?”

Person 2 - “bro, you have brain rust”

———————————
Person 1 - “You can’t use the word ‘fat’ it’s offensive”
Person 2 - “I think you’ve got some brain rust bro”

brain rust by Sav 7 May 24, 2023