acronym for "does it matter?".
Meaning "irrelevant" and used mostly in gen-Y internet slang/ IM conversations, "DIM" is mostly the end of a smirk comment, to specify that the info provided does not matter at the current context.
dude1: Hey, it was cold here. Look at these pics of icicles!
dude2: location?? I could spam u with pics from my Antartic expedition. DIM?
dude1: ha. These are from Orlando, Florida man! It was cold this year.