The word dag(gy) was previously mentioned on LLOG, but at first I didn't grasp what Lottie meant.
The OED has this for daggy:
N.Z. Of a sheep or wool: clotted with dags.
slang (orig. and chiefly Austral.). Freq. depreciative. Dirty, scruffy. In extended use: contemptible, unacceptable; (esp. among schoolchildren) unfashionable, unattractive, socially undesirable.
From this cartoon, as well as from Ray Girvan's comment back in 2009, I infer that the colloquial usage has become widespread in the U.K. as well.