It as bound to happen eventually - Derpy!
She may be only a 'background' pony, but she's earned herself quite a fandom! I can't say she's my most favorite (that distinction goes to Fluttershy), but she's got her charm.
Anyways, I went with a more basic background for her here, and I think it came out quite nicely. I think her expression is pretty damned cute too ^_^