I would use terms like "team cancer", "not a team player", and "freakishly mental nutcase" but I think those terms are already in your subconscious when pertaining to him.
from what I know he's simply just a hothead. much like Jose Guillen. except he's a much better hitter.
when he was with the Dodgers he didn't get along with Jeff Kent and called him a racist, or something like that. but Jeff Kent is an jerk, from everything I've heard. the deal was Kent didn't like Bradley, and Bradley didn't like Kent.
beyond that I haven't heard of anything that would make him a "team cancer" other than sensationalist arguments from forum posters, basing their entire opinion on his on-field tantrums. not just you, but on other forums as well.
then again, I don't really know him that well.
and the incident in san diego, from what I recall that was a long-running thing with that same umpire. the ump freaked with him earlier in the season, and then freaked with him again and he snapped. but I don't know all the details behind it.