Eat their hearts
Screaming 'eat your heart out' is like saying 'screw you, I hate you.' It’s the worst insult you can give someone who already hates you.
My friend said 'eat your heart out' after I stole his lunch. He cried.
My ex said 'eat your heart out' when I broke up with her. It was the best part of the breakup.
I told my dog 'eat your heart out' when he ate my homework. He looked guilty.