Dingy:

din·gy [1] (dĭn'jç)
Darkened with smoke and grime; dirty or discolored.
Shabby, drab, or squalid.
[Possibly from Middle English dinge, dung, variant of dung. See dung.]

ding·y [2] (dĭng'ç)
adj. Slang.
Crazy; insane.

Atomica doesn't give me any etymology for this, but I'm not seeing a clear connection from dung.

Howzat?