Toxic thoughts could be very debilitating. First area I would suggest looking into is what are the circumstances that thoughts of these people come up with you? Are other people in your life bringing their names up? Are they people in your life who you blame for missed opportunities? Depending on the transgression they did to warrant your negative feelings, would determine how you address this issue. If there was a significant issue that warrants your hatred, such as sexual abuse, it may require a different approach. If these individuals are someone you blame for your current situation and feel stagnated because of them, your preoccupation with them is serving as a deterrent to moving forward. Identifying the function or purpose of these thoughts would be a productive first step.

I would suggest the next direction to go, if you recognize that these are not thoughts that would warrant the attention mentioned above, we identify these thoughts as intrusive, counter productive, and irrational thoughts. Picture yourself as a gatekeeper. If you allow certain thoughts to enter, you are opening the flood gates to more thoughts. Do not give these thoughts credibility. By externalizing these thoughts, it gives you a better chance at dismissing them before they gather up momentum. If these thoughts become more problematic and don't go away, it may be helpful to seek out further assistance to address them more aggressively.
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