DCM means Disney Channel Moment. If you suddenly find yourself in a situation that seems like it could be made into a cheesy Disney Channel show or you say something like "Thats totes awk" You can use the term DCM.
Example 1:
Kimmie: Hey Kandie, did you think the dance was a major Blow or Go??
Kandie: Major Blow! Did you see Tammie dancing? Scandelous!
dcm is the owner of the radiance message boards, as well as the programmer of its source code. He owns uberleet.us, and what used to be hazelhood.net. His younger brother, "Hiei", is notorious for hacking numerous spinoffs, including one of Mikhajist's old message boards.
"Mikhajist is a worthless french faggot who does not know how to code."
-dcm
As you can see, I have put all three definitions into a single quote by him.