In high school, some of the guys who picked on me started calling me "Dewey". Their tone of voice made the nickname an insult. My baseball coaches picked up on it and started using the name as well, but without the condemnation that came from my peers. As a result, I took the nickname from my coaches because it became linked to something I love, and because I honored and respected my coaches.
2k comes from trying to register "Dewey" as an e-mail address. It had already been taken, so I added 2k for the year 2000, and it worked.