There have been a lot of X-Men over the years, and not all of them are going to be fan-favorite heroes. For every iconic hero like Nightcrawler who perfectly represents the themes of the series, there's a lesser mutant like Maggot waiting in the wings. However, only one mutant has been explicitly called the "worst X-Man ever" by Marvel itself.
That unlucky hero would be Bailey Hoskins, the main character of X-Men: Worst X-Man Ever by Max Bemis and Michael Walsh. This 2016 miniseries is the only appearance of Bailey, a young mutant with an unfortunate power and lethal side effects. Still, despite his title, he actually did have one noble moment and proved why he belonged alongside Marvel's other mutant heroes.
Who Is Bailey Hoskins?
Baily was living his life as an average American high school student. One day, his parents revealed to him that they were both mutants who were quietly living in suburbia, and it was likely that he would eventually develop his own abilities. Bailey was initially excited by the prospect to join the "awesome" X-Men, and just got more and more pumped as he formally met the team. But all of that excitement faded away when he learned his powers: he has the ability to supercharge his body and explode. But there's no reconstituting or regrowing for Bailey. If he explodes, he's dead.
As Bailey points out himself, it's not exactly a great power. Deciding that he basically has no power at all, he decides to return to his basic human life with his parents. But as they leave the Xavier Institute, a Sentinel attacks and crushes his parents in a single step. Although the X-Men stop the Sentinel, Bailey can only sob as he can't even do anything to help. With nowhere else to go, Beast invites Bailey to move into the Institute and become a student.
Worst X-Man Ever
Bailey tried to adjust to the school, but he was quickly overshadowed by the fantastic abilities of his fellow students. Forge attempts to build an exo-suit for Bailey to use in battles so he could fight alongside the X-Men in times of crisis. However, an over-eager Bailey wore the suit into battle and terrified an attacking Purifier. The Purifier sued Bailey for emotional damages, costing the X-Men a great deal of money and Bailey the respect of his peers. Beast tries to find a place for Bailey by making him an intern for the various other X-Men teams, but none of them were a good fit.
Bailey did find one brief flash of friendship in Miranda, a fellow young mutant who has the ability to make things stop (or resume) existing. Bringing her to the Xavier Institute, she's determined to be an Onicron mutant, an entirely new level of power above even Omega mutants. As a caveat of her joining the X-Men, she requests that Bailey be put on her team.
Working with fellow students and brother-sister duo of Rags (who can degrade physical objects) and Riches (who can turn things to solid gold), Bailey becomes a glorified water boy for the squad. Things only get worse when Mystique blackmails him, ordering him to assassinate Charles Xavier.
When Bailey hesitates, Magneto kidnaps Bailey and tries to force him to work with the Brotherhood. When he's given the chance though, Xavier reaches through to Bailey. But then Riches uses his powers to turn Xavier's insides to gold, revealing himself to also be an agent of Magneto and killing Xavier himself.
WHAT HAPPENED TO THE WORST X-MAN?
Riches take the opportunity to become a world-conquering mutant, usurping the old guard of X-Men to make himself the ruler of the world. Despite the efforts of an X-Men team led by Iceman, Riches ended up winning, and many of the remaining X-Men lead dark and depressing lives in the future. Beast is in exile and has mutated further, and Colossus fights in a mutant fighting league to try and save the life of Kitty Pryde. The Brotherhood and the Hellfire Club have become successful, although Magneto and Quentin Quire have been abandoned and left destitute.
The story jumps ahead decades when Bailey is recounting his life to a documentary. As a sign of mockery, Riches invites Bailey to an annual celebration, and Bailey decides to attend.
Arriving at the ball with a plan, Bailey runs into the older Rags (who is now dating Gambit) and Miranda (who hadn't aged a day since he last saw her.) Miranda revealed she was the one responsible for maintaining the ever-expanding continuity of the Marvel Universe. She's partly responsible for the sliding timeline of the Marvel Universe, retconning the universe in small ways when she feels the need to. In the end, Miranda needed Bailey to show up so he could complete his story. Bailey finds Riches and destroys both of them in an explosion, ending his reign. Confident that he's played his role, Miranda retcons the universe once more. Bailey may have been the worst X-Man ever, but even he got one moment of nobility in the end.