Phrase "take it out on someone" means to make someone really tired. In my mind it means to release your anger on someone, like a defense mechanism( projection maybe). For example..your friend fell out with her boy and now she is very irritable and rough with you. So you'll say to her "You may tell all this to your ex but don't take it out on me". That is all ))

I agree with Tashuna. "Release your anger on sombody (who doesn't deserve it)". Or, To punish sombody for something (usually something that he had nothing to do with).