A sexual display undertaken by men.. To strip naked and swing yours arms back and forth as if you are running while standing stationary, causing the hips to twist and the penis to slap against the thighs. Once the running man is sped up to a sprinting pace, the slapping sound of the penis on the thighs becomes impossible for women to resit.
James - "Bob managed to pull that 10/10 bird at the club last night"
Rico - "How'd he manage that?"
James - "I heard he showed her the running man in the disabled toilets"