According to Aunt Alexandra, Bob Ewell bears "a permanent running grudge against everybody connected with (the Tom Robinson) case". Atticus agrees with Alexandra's assessment.
Bob Ewell sees the world at large as his enemies, and he specifically hates everyone connected to the case. He had thought that winning the case would bring him fame and respectability, but it did not. Tom Robinson was convicted only because the people could not overcome their deeply ingrained prejudices against blacks to uphold justice. In reality, "very few people in Maycomb really believed (Bob Ewell's) and Mayella's yarns". Instead of being a hero after the trial as he had hoped, Bob Ewell came out looking like a fool.
Bob Ewell is the type of person who never takes responsibility for anything. After the trial, he did manage to get a job, but lost it after only a few days because of laziness. He then blamed Atticus for "getting" his job, and began to undertake small acts of intimidation against individuals who were involved in the case to express his bitterness. He cut the screen on Judge Taylor's porch one night when the old man was home alone, and terrorized Helen Robinson, Tom's widow, as she walked to work each day.
Bob Ewell is a degenerate, good-for-nothing character who will never take responsibility for his own actions, and the fact that he won the trial did nothing to change that in the eyes of the townspeople. Instead of examining his own behavior, Ewell blames his situation on everyone else, looking at them as his "enemies" (Chapter 27).
Bob Ewell bears a grudge because nobody in Maycomb truly believed him and Atticus made him look like a fool on the stand, contradicting him and Mayella.
Ewell sees the judge, the sheriff, and Atticus as his enemies.