If you're a fan of the big two comic publishers then you have long since made peace with the concept of reboots. They've long since become associated with the marketing ploys thinly disguised as narrative shakeups meant to spike up the numbers by completely overhauling every single book in either DC or Marvel's universes. Marvel's done it about once on that scale by now, while DC has done it quite a bit more.
However, a reboot can mean any amount of change to the status quo of a character's universe. The only criteria is that it has to be a reset to zero, whatever form that takes. As such, there have been reboots for characters both big and small. And because there are so many of them, there have been - of course - some MASSIVE stinkers.
Whether because the idea of the reboot was sound but badly executed, a terrible idea from the get go, or the character was doing just fine and didn't NEED a reboot, these superheroes have never been the same ever since editorial decided that the backstory and development their writers had been painstakingly building up was for dumb nerds.
10. Iron Man
Tony Stark is already considered to be obnoxious enough, so it's doubtful turning him into a teenager would have fixed this problem.
This reboot comes to us courtesy of the Avengers storyline The Crossing, in which our original Iron Man was revealed to be a bad guy working for Kang this whole time. If that makes absolutely zero sense to you, good, you still have all your brain cells working, so carry on as normal.
Anyway, to make a long and very dumb story short, defeating Kang requires the aid of Tony Stark...from the past. When he was a teenager. Who they then let stick around because they're already letting the space time continuum die in a pool of its own blood, why not kick in its teeth while it's down?
This reboot of the Iron Man story had teenage Tony Stark take center stage, seemingly to appeal to a younger audience. Which, like a similar later attempt - the cartoon series Iron Man: Armored Adventures - blew up right in their faces and didn't last long at all.