How do you pick a fight back up after the other interrupted it by walking away?

A punch in the throat usually works

Throw a shoe at them

“So, where were we?”

Show off by flying their helicopters driving around wearing their equipment and demanding recognition of your government.

I shout "[b]AND,[/b] YES UR FANNY FLAPS REEK" before strutting away myself.

It's the only reasonable thing to do.

Wait till they calm down and are having a good day then take up where you left off 😝

Clocking them in the back of the head with whatever is at hand.