They tend to be quick to anger and to violence whether that be violent speech or physical violence. Another sign would be a fixation on causing harm to a specific person or group of people till it eventually consumes everything else only leaving their hate behind.
I think that those who insist on continuing an argument until their opponent is beaten down or those who simply will not change their mind have a lot of hate. They don't change their mind because they hate their opponent and changing their mind would mean they lost the argument. This hurts their pride, so they don't change.