Tony Pena

Unfortunately in Pena's case, the effectiveness of his first big-time managing gig left much to be desired:

He showed little to no feel for knowing when a pitcher still had something left in the tank or was completely out of gas.

He repeatedly made a punchless offense even more punchless by ordering his players - sometimes his best players - to lay down sacrifice bunts in non-game situations.
The 25-man roster was managed as if all 25 guys were just generic baseball players with no differentiating qualities, which is why Desi Relaford received nearly as much playing time at a corner outfield spot as more-productive hitters like Matt Stairs did.
Relief pitchers who were pitching well (Jason Grimsley and Andy Sisco come to mind) often received no rest, sometimes pitching three days in a row. As a result of that abuse, Grimsley broke down in the second half of 2003, and I'd bet that Sisco - he of the dead arm late last year - could do the same once we hit the dog days of August.
The list goes on and on.

Pena quits! I feel a bit cheated. The only thing I had to look forward to this season was Pena's humiliating public dismissal, but I suppose this will have to do . . .I don't there's much reason to rehash Pena's troubled reign in Kansas City. He was a terrible in-game micromanager, placed way too much importance on gritty-yet-highly-unproductive players like Desi Relaford, etc. In the end, though, the Royals of 2002 to 2005 simply weren't very talented or experienced, and despite the 2003 miracle fluke, Pena managed teams that were destined for 100-loss seasons no matter his or any other manager's interventions. Pena simply made it worse with his nauseating sunniness and had aggravating in-game skills.