He's 'resentful' of his boss. = He feels 'resentful' toward his boss.
She is 'resentful' about being demoted.
a 'resentful' letter to the editor
(..) you know what it does for the traffic. So, when you say you're concerned about him, you actually are concerned? Yes, of course. It actually is a childish feud? He's always been so resentful. You can imagine the Christmas dinners. Yeah... No... God, no. I'd better, erm... Hello again. - Hello. (..)2010 TvShow: Sherlock Title: A Study in Pink Season: 1 Episode 1