Well , i also struggle with blocks , one thing i would recommend doing is to just say the word “boss” for once , ignoring the reaction of others while saying it. Maybe who knows it might not be as bad as you think. Our minds are instinctively programmed to anticipate the worst (maybe helpful for survival but certainly not in the case of speaking situations) The only thing that you are doing while substituting another word for this one is fueling your associated fear with this specific word. The Same applies to any other feared words that you might have. Stepping out of comfort zones once in a while works plenty especially in desensitization.