Any event where males try to prove their worth by comparing their (often irrelevant) possessions/attributes, especially when size is involved. Good examples are the comparisons of engine or salary sizes. This meaning originates from the idea that he whose penis is larger is superior; primitive males would 'waggle their dicks' to show whose was bigger.
Reporter: President Johnson, why are we still fighting the war in Vietnam?
LBJ: (unzips his fly, draws out his substantial organ): This is why!
Onlooker 1: Dude, that guy just whipped it out like LBJ! It's like the whole war is just a big dick waggling contest!
Onlooker 2: That IS LBJ, fool.