Doing or saying something in a bitter, angry way, especially when you feel you've been treated unfairly, is to do it resentfully. If you get a bigger piece of cake than your brother does, he may glare resentfully in your direction.
When you're resentful, you're indignant or spiteful — and to act this way is to behave resentfully. When you feel bullied into doing something, you'll do it resentfully. And, if you know your grandmother gave your sister a new laptop for her birthday, you might accept your gift — a magazine subscription — resentfully. This adverb comes from resent, "feel bitterness or indignation at."