Must have mental illness/phobia, Ideas?

[Mr Beer]

Pyromania, because lighting fires makes any situation more interesting.

Split-personality disorder could be fun, invent a personality of the week, change every episode. Silver age superhero heroic one week, Marvin the Paranoid Android the next, then Roger Irrelevant, then Pennywise the Clown...plan half a dozen in advance.

I feel like a lot of murderhobos are basically serial killers anyway so that's a surprisingly dull choice. So are things like sociopathy and narcissism, many characters have low empathy and selfishness dialled in.