An intensified way of saying bet, when you wanna say bet but with a lot of emphasis, like when you're in an argument and feel the need to yell bet, but can't show emotion in text.
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.