A vulgar reference to an: idiot, moron, jerk. Used to convey the mental image of a man metaphorically described as a wadded-up ball of a tallywhacker (otherwise known as a penis).
Good sir! You have just applied your forefoot to the top of my heel and unearthed my foot from its leather placing! I inquire an apology, post-haste, dickwad!
An insult. Basically a wad of broken, discarded dicks. Not only are you calling someone a dick, you are calling them a big ol' pile of dysfunctional dicks!