Mikal: Hey Jay where are you going?!?
Jay: I had too much coffee! I got a turtle pushing cloth!
Mikal: BROWN DERBY!
Its derivation is twofold. The least graphic metaphor being that the purple helmet may take on a brown hue during the act. The second centers around the word Derby, in the context of a demolition derby where two objects are rammed into each other causing some amount of damage to the object with less momentum.