Sentence:  “I Love Lisa” opens with one of my favorite underappreciated running jokes from "The Simpsons": the passive-aggressive, quietly contentious relationship of radio jocks Bill and Marty, whose mindless happy talk regularly gives way to charged exchanges that betray the simmering <WSD>resentment</WSD> and disappointment perpetually lingering just under the surface of their relationship. 
Meaning of the word marked with <WSD> tags:  A feeling of anger or displeasure stemming from belief that one has been wronged by others or betrayed; indignation.