They make two big confusions:
1. They confuse "How can I help this prospect/customer?" with "How can I get rid of this person and get back to work?"
2. They confuse, "How can I have a better day by treating this person with a great deal of respect?" with "Why isn't this person treating me with the respect I deserve?"
Toxic employees are usually afraid, poorly managed and underappreciated. They can rarely be bullied into changing their behavior, often because they themselves are bullies. Managers can hire the non-toxic, re-assign the toxic and be really clear with themselves that they're willing to pay almost any price to keep toxic employees away from everyone else. And if toxic employees appears to be a pattern, my bet is that it's your fault, not the employees.