The traveling secretary was the old person I was referring too. I do remember the Youk spat, but I'd hardly call that a headcase move (I don't remember any punches thrown, though. If you have a link, share). Arguments happen. Just today, BJ Upton and Evan Longoria on the Rays got into a tiff in the dugout. I wouldn't call either of them headcases. I wouldn't call Jeff Kent a headcase because he got into an argument with Bonds a while back. But when a player continually beats up gatorade containers and risking injury to himself (Zambrano), I'll have to pass.
Manny just doesn't care (while also showing harmless mental lapses), which is more laziness than being a headcase. Quitting on the Red Sox was a <dick move, yes, but hardly fit for a straitjacket, unlike Zambrano who blows up at least 3-4 times a year.