When an individual finds it incredibly difficult to converse or interact with a person of the opposite sex.
Also occurs when an individual can interact with a person of the opposite sex, but speaks without thinking, offends them without knowing it, or just doesn't know how to treat them. This can be seen in terrible boyfriends/girlfriends, pimps, annoying nerds, and short white freckled kids who think they're tough.
Hottest Girl in School: Hey, um, I don't remember ever seeing you before...
Justin: yeah um that's cus i'm always behind you... wait no i mean...
HGiS: Ew! Get away you freak!
*justin runs back to friends*
Friend: Omg man, do you have OSSD or something?!
Justin: What's that?
Friend: Opposite-sex social deficiency. You can figure it out.