When someone spends the night over a friend's house and right before they sleep they take their own socks off. Later the next day, when they leave, they either forget their socks or just don't give a shit about them because they're too sick of hanging out and do not want to spend another second over that person's house. Shortly after you meet up with that friend and discover he or she is wearing those socks. Called a Sock Pirate because pirates take things and make off with them as their own.
Bill: Gosh Don, I hate to point this out but those are my socks.
Don: Ohh, your right. Sorry man my mom kinda bleached them.
Bill: Well you better get me a new damn pair or I'm willing to tell everyone your too poor to buy your own pair, you Sock Pirate.