It really can be very confusing even for professionals. I have known a number of people, men and women who had bipolar, it was called manic depression back then. Some of them were easy to diagnose or tell, some however get very aggressive, anger and have fits of rage, which could also make you wonder if they are schizophrenic. Now I've actually seen personally a friend of mine, a girl, who was off her meds for 6 months. She is most definitely a bipolar. However, she also was a heavy drinker and substance abuser too. In her Manic periods, she could have mood swings minute to minute! One minute a sweet little angel, the next yelling profanity that would embarrass a truck driver! Her manic episodes were all over the map! She could easily be confused as one having BPD. I would imagine that the opposite might also be possible too. Just saying, it really is not so easy some times, and unless your hospitalized for a few months, it's mostly guess work even to the most trained eye. Even folks with bipolar have mood swings minute to minute in a manic state, not all but a significant number of them can be all over the map in a manic state, not just in a up state.