Short for Digital Autoimmune Deficiency Syndrome, or Digital AIDS. A form of AIDS "contracted" by being too close that you consider disgusting. Many sub-classes exist, including Counterstrike D-AIDS, the most common form.
0MG! I AR3 T3H 1337 PWNZ4R5!!!111one1
Dude, don't touch me. I don't want your D-AIDS.