Mine is the initials of Off Kilter, one of my favorite WDW pastimes (and it was through an Off Kilter forum that I came to find the DIS in the first place.)
With the exclamation point, though, it reminds me of the Chipmunks Christmas song (I think it might be "Please, Christmas Don't Be Late"), the one where Alvin has his own part to sing but needs to be reminded when it's time. In one verse, Dave says, "Alvin.......Alvin.........
ALVIN!!" to prompt him and Alvin yells, "O
kay!" in this irritated voice and starts singing.
I think I probably should've just left well enough alone and stuck with the first explanation.