The absolute worst villain of the Marvel Comics hero Ant-Man is a mad scientist known as Egghead, and while Egghead is an established Ant-Man antagonist, it's Hawkeye who holds a major grudge against the ridiculous villain. Egghead is regarded as Ant-Man’s worst villain because he is clearly ridiculous with the ‘mad scientist’ schtick shared with a number of better villains across the Marvel Universe. Plus, Egghead’s schemes almost never work as he was always taken down easily and pathetically by Ant-Man, though one villainous plot that did work out for the villain unleashed the wrath of another Avenger. The reason behind Hawkeye’s hatred of Egghead lies in the first volume of the Avengers comic series in which Egghead commits an unforgivable act against Hawkeye and his family.
In Avengers #64 by Roy Thomas and Gene Colan, Egghead's hatching a villainous scheme regarding a deadly space station that he needs help funding. The villain approaches Hawkeye's brother, Barney Barton, to join him on his venture, an offer Barney refuses. So, Egghead launches a small army of robotic soldiers to capture Barney and force him to comply, though when the Avengers get wind of Egghead’s evil plot, the team springs into action to stop him. While the Avengers do what they can to stop Egghead and save those he captured, they were too late to save Hawkeye’s brother who was tragically killed by the Ant-Man villain.
After Egghead killed his brother, Hawkeye developed an intense grudge against him which the Avenger carried with him from that day forward. When Barney lay dying in Hawkeye’s arms, the two exchanged a heartfelt brotherly banter that gave fans a brief look into their history. Hawkeye was trained in the circus and became famous long before he became an Avenger for the skills he exhibited that would later be refined into superhero abilities. Barney tells Hawkeye that he had always been a little jealous of that fame but that, now in his death, he may finally get a moment in the spotlight. When Barney dies, Hawkeye screams out in blind rage, vowing to get revenge on Egghead for what he had done.
Lucky for fans, they didn’t have to wait long for Hawkeye’s vow of vengeance to play out. In the very next issue, Avengers #65, Hawkeye hunted down and captured Egghead and brought him to justice all thanks to the new powers he acquired during this run. Hawkeye was granted the suit and powers of Giant Man with the technology it takes to make him grow big along with the serum necessary for one's body to survive the transformation. Hawkeye as Giant Man was able to quickly capture Egghead. Even though justice was served Hawkeye’s grudge still remained.
Egghead killed Hawkeye’s brother, a wound that would not easily heal even though Hawkeye brought Egghead to justice. From the moment Egghead committed that act of unspeakable villainy against Hawkeye and his family, he was forever hated by Clint Barton. Plus, the fact that Hawkeye used Giant Man’s powers to stop Egghead is just poetic as Egghead is famously a villain of the original Ant-Man/Giant Man Hank Pym. Even so, Hawkeye’s grudge against Ant-Man’s absolute worst villain will never go away as the normally ridiculous Egghead killed someone Hawkeye loved.