Drain the main brain
Similar to drain the main vain, however as we all know, cum is stored in the brain.
Timmy: “Hey Billy, what were you doing in the toilet last night? Sounded like you were role playing a rapidly declining dragon trying to climb a jagged rock!”
Billy: “ah sorry about that, had to drain the main brain”
Timmy: “lucky bastard!”
Billy: “ah sorry about that, had to drain the main brain”
Timmy: “lucky bastard!”