It may seem strange to include a team of heroes on this list, but the X-Men and The Avengers are far from pals. The tension between the two teams reached its boiling point a few years ago in the divisive Avengers Vs. X-Men storyline which saw Cyclops and his fellow mutants declare war on Captain America and company when they arrived at their home to take away the incredibly powerful Hope Summers. Despite the majority of fans being on the side of the X-Men, they were ultimately the ones portrayed as the villains here, especially when Cyclops, Magneto, and a handful of other mutants were given the powers of the Phoenix and used that to take over the Earth (turning it into a better place, something The Avengers were none too keen on for some reason). Even now, the wounds from this battle are still fresh.
