Why do some ex's turn mean and nasty after a break up?

[intherough]

Just that really. I could never imagine saying some of the things my ex has said.

I blocked everywhere possible but they messaged on something I didn't know I had so read a few messages.

To hurt you? Just ignore…

Narcissistic rage. Ignore completely.

Depends why you split up really doesn't it?
Context?
There's all sorts of scenarios, from splitting with someone perfectly amicably to bedding his best mate or worse or anything in between.

Emotionally immature and can't handle the break up?

Because some people are vindictive, petty and spiteful. So they'll do anything to get back at you if they feel they were wronged or that you're 'winning'.

It's a difficult situation sometimes and as mentioned depends on the circumstances in which the relationship ended. My ex has remaried and and on the surface has it all, beautiful house, great husband...money in the bank retired at 54. Yet she's still hostile to any girlfriend or partner I've been with. Unfortunately some people are never happy and are never able to really move on.

Because they always were mean and nasty and when things don't go their way they can't hide it so well.

It depends. Some people are in the family of narcissistic personality. Cheating is also always very hard to take as it's not just a break up due to incompatibilities, it's a betrayal.

Depends on the context..... Did you sleep with his best mate? In which case the abuse is to be expected, if it was for no reason and both amicable then I have no idea

I think it's because sometimes people make a lot of compromises in a relationship for the benefit of the relationship and if the other person ends the relationship it can feel as though their only concern was their own situation or feelings and they didn't try and fight for the relationship. Then there's hurt and anger.
It's not always about mean and vindictive behaviour it's about pain.