Acronym in the sports world for "Did Not Finish". Ironically, however, the #1 Vaporware of all time, "Duke Nukem Forever" (known also as "Duke Nukem Taking Forever", ".. If Ever", ".. Whenever") coincidentally has the exact same acronym.
To suffer inexplicable pain of some sort. This pain isn't necessarily physical, however. The usage of the word "world" doesn't always implicate a great length of time that the pain will exist, but rather the magnitude of the pain.
I spent my first year of college drinking and failing classes. Now Daddy won't pay my tuition, and I have to go to community college. I'm in a world of hurt!
Dad: Son, did you go outside without my permission again?
Son: (lying) No, Mom said--
Dad: *removes belt* You're about to be in a world of hurt!
Son: *starts crying even though he hasn't been hit yet*
Dad: Why are you crying? I haven't even hit you yet! But don't worry, i'm about to give you something to cry about.