If a guy calls his ex-girlfriend “crazy”, run away. Seriously, don’t even waste your time because there is no point. It is a huge red flag and you should be aware that chances are high that you shouldn’t be seeing that guy at all. Let’s explain why.
First of all, whatever version he is giving you has to have another side of the same story. The fact that he wouldn’t be so objective about the story says a lot.
Also, this could be his way to dismiss questions on his past. If he described his ex as crazy he knows you won’t ask too many questions about her or what happened. It’s a very easy strategy to use.
Finally, he is probably playing the victim. Whatever crazy thing happened was probably a reaction to his behavior or to something that the two of them did. So the best thing to do would be to take responsibility but by playing the victim, he demonstrates not to able to do it. Long story short, either he is hiding something, or he is not being respectful to his ex or he is playing the victim part. Wouldn’t it be better to date someone else?