This is somewhat redundant I guess since so many people have mentioned these guys, but here goes:
Jimmy Haynes - Here's a guy who has good AAA stuff and terrible MLB stuff. Yet, the Reds make him their Opening Day starter. What else could have happened except a disaster? One fluke season does not change the fact that he is absolutely mediocre. I would much rather take a chance on an unproven rookie than a pure stiff.
Jim Kern - Jerk. If you don't like playing in Cincinnati, it's because the fans have turned on you for being a jerk.
Alex Trevino - To me, Trevino was the only supposedly talented player we received in turn for dumping our entire starting OF after the 1981 season. In reality, he probably had no chance to be successful on that team, but his skills were poor and the fans hated him. He was no Bench, but heck, he wasn't even LaRue either.
Ron Oester - Someone with Oester's physical size and skills should surely have been able to get more out of himself right? Career high in doubles = 26, and career high in HR = 11. Don Gullett had a better swing than him.
Bob Buchanan - Couldn't break a pane of glass with his fastball, but he was ticked that he didn't get his call to the majors much earlier in his career. His stats when he finally did get to Cincinnati were 8.44 ERA with a 1.91 WHIP.
Personally, I doubt have too much of a problem with players who flop (Wille Greene was mentioned previously), I get more frustrated with players who give it away because of their attitude or inability to change (Kern/Oester) or who shouldn't have been in the bigs in the first place (Haynes, Trevino, and Buchanan).
My honorable mention is Hal Morris. My gut tells me he hit .300+ in the first five innings, when the Reds were up or down by 5 or more runs, or the pennant race was over. I bet he hit sub .200 after the sixth inning in close games. Exactly the opposite of Tony Perez.