At first I thought this was a case of a driver, who was running late for work, trying to figure out where in a pickup truck he could legally lock his gun up while at work, then, in a potential stoke of brilliance, he thought to just toss it out the window.
Then, on second thought, maybe he was trying out a new mosquito control technique that one of the mosquito board candidates might have proposed, where by in the early morning hours, in lieu of spraying insecticide over a given area, they would spray hot lead. (Note to self: with the size and aggressive nature of some of the mosquitoes in the area, high powered rifles may be better option).
Third, that he was multitasking while driving on 30A, as so many of them do, so he had one hand on the gearshift, one of the cell phone, one on his cigarette, one on his beer, and one on the radio knob and one on his gun, so when he tried to wave back at the bikers, it was his gun hand that was closest to the window.