Action Bronson -- I Might Have Deuced During Port-a-Potty Performance

Action Bronson finally reveals the big secret ... what he did behind closed doors -- specifically, whether he dropped a deuce during his infamous port-a-potty rap performance?

TMZ posted the epic clip ... showing the "Shiraz" rapper ducking into a port-a-potty during his performance at the Ottawa Bluesfest ... and not missing a beat.

In addition to addressing #1/#2 matters, he also unveiled his plan for topping that stunt.

It won't be pretty.