This is so subjective. Some of the traits that some, even most, might consider "bad" are traits that some others, including myself, might consider "good."
For example: Dr. Russell in TNG's Ethics is a brilliant, driven researcher who achieves amazing results. Her talents combine cutting-edge, outside-the-box medical theory and its surgical implementation. She is clearly supposed to be reviled by the audience for her abandonment of medical ethics when the opportunity presents itself. I find myself torn about her, though, and notice that it's not as if she runs Dr. Frankenstein's House of Horrors--she uses those who are already dying for her research and, in Worf's case, someone who, although emotionally distraught, IS in his right mind and DOES give permission for an experimental procedure, the second of which is something that is done in the real world.
For some reason, though, my mind comes back to Admiral Ross. Not sure why--maybe because he is very likable? That alone shouldn't be enough.