Bad-tempered, sulky (6)
(Other definitions for grumpy that I've seen before include "short one" , "likely to snap?" , "animated little miner" , "One of Snow White's Famous Seven" , "In a bad mood" .)
(Other definitions for sullen that I've seen before include "Surly" , "'Grumpy, resentful (6)'" , "Dour" , "Bad-tempered and sulky" , "Gloomy and bad-tempered" .)