Have you got any qualifications?
http://accesstocompletion.com/100mg-doxycycline-for-acne.pdf#according ">what is doxycycline 100mg tablets used for Or, if all else fails, you may need to simply warn prospective new employers that the reference won't be a good one, which will allow you to provide context and framing for what they might be about to hear. For instance, if your relationship with your boss soured after a particular event, you could say something like, "By the way, I had glowing reviews from my boss at that job, but our relationship became strained toward the end and I worry that it could color that reference." (Be prepared for questions about what caused the strain.)