How can you tell the difference between someone who is insecure and jealous of you and someone making fun of you, well cause it's easy and they can?

I know people have a tendency to pick on those considered weaker, less competent and immature than them but there are those who do it out of sheer pride because bullying someone gentle and naive is their idea of fun and some do it 'cause they are spiteful of everything that's right in you and desperately and obsessively needs to point out your flaws to give them a sense of satisfaction? Now how do you differentiate between someone who picks on you for being insecure and jealous of you and someone who knows you're stupid and annoying you is simply entertainment for them?
How can you tell the difference between someone who is insecure and jealous of you and someone making fun of you, well cause it's easy and they can?
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