Yeah, my worst was a Rule V - let a former first round pick go, and it wasn't that I even forgot about it entirely, I set him up to be protected but then didn't submit the transaction, so it was still sitting there when the roster freeze occurred. I wound up fleecing the guy who drafted him in a trade to get him back, and he didn't wind up being all that special anyhow (pretty sure I released him in his 3rd arb year because he wasn't worth that kind of contract), but still a pretty dumb move.