You can't really "train" BPs. Their behavior is a product of their environment and how secure they feel. Things that affect this are their enclosure and hides (ample hiding space is very important), temperatures and humidity, and regular access to food and water. Most BPs that you might classify as "mean" are usually lacking in one of those areas and once corrected, become "puppy dog" tame.
Remember, they may appear to act like puppy dogs and they certainly are cute, but BPs are very simple creatures and do not show affection the way a real puppy dog can.