People get insecure a lot. They would get you to your limit for no reason but insecurities. Simple or vague, you'll know it when they treat you sarcastically. And although it’s not something new, they get to your nerves. Not until you give them a dose of their own fatal medicine that they realize they have done enough. Funny thing is when they taste the bitter truth of what they do to you; they aggravate especially when ego was stricken. If you can't handle the waves, then don't swim in the ocean. It is always a fair warning to dive at your own risk. It is immature to pick on someone; more so, to get easily aggravated when the bullied fights back.
We all strive to be better in what we do and when someone makes a mockery of it, it becomes magnified even more. Especially when they strike your source of living.
The best thing to do, if you can't say anything nice, just shut up. Insecurity is deadly. As they say, resentment is like drinking a poison and waiting for the other person to die. Whatever you do really gets back on you.
So if you know someone who succeeds in what they do and you don't feel good about it, it is best to say nothing at all. If it will be too hard to compliment, let alone support, just say nothing. Rather than blurting out half meant mean mocking jokes, focus on what you can do to make yourself better.
We all have insecurities; the difference is how we handle it. Would you be immature and act like a bully or focus on letting yourself grow to fill that empty part of yourself.
The later makes you better the previous ruins you.