showing a brooding ill humor; "a dark scowl"; "the (Atasözü)ially dour New England Puritan"; "a glum, hopeless shrug"; "he sat in moody silence"; "a morose and unsociable manner"; "a saturnine, almost misanthropic young genius"- Bruce Bliven; "a sour temper"; "a sullen crowd"
Someone who is sullen is bad-tempered and does not speak much. The offenders lapsed into a sullen silence