I find direct confrontation is best. Especially is several other co-workers feel the same way. Confront as a group. Maybe confront isn't a good word. But I go directly to them with the problem in a non-confrontational manner and I never give my opinion but the general consensus. If they ask me my opinion they get it. Both barrels.
I agree with MB. Address the situation sooner than later and remember that documentation of SPECIFIC examples with dates goes a long ways. Avoid backing someone into a corner to prevent putting someone on the emotional defensive.
I would add that staying with facts versus opinions helps keeps it less judgemental.
Once the issues are identified, immediately moving toward a solution, how to monitor if the solution is working and how to change if the solution is not working tends to focus energy towards the future versus dwelling on the past.
