It is impossible to get this achievement without reading
http://www.gamefaqs.com/console/xbox360/file/932035/51343 . The method is tedious and time consuming, but it absolutely works. Be aware that some of the taunts are virtually identical (like the "ogre's loincloth") but have opposite defenses.
Personally, I tried blocking but it takes forever because Bertrand loses so little when you block him, and you lose a lot if your attack fails. Eventually I changed my strategy and did nothing but parries. Sometimes it was pretty close. If you are almost out of health and don't think you can win the duel, turn off your Xbox. When you start the game again you will be at exactly the same percentage. You won't lose points or your progress.