"Go away." - To many people in real life frequenntly.
Also to many people both in life and online: "I know you think you're logical and intelligent, but you have no freaking idea how illogical you are being right now, are you? I know you aren't listening to me because you cannot fathom the idea that YOU, wonderful, rational YOU can possibly be so irrational that a self-admitted / diagnosed emotionally-driven / irrational person can pick up on it. Also, you think you are being compassionate, but you're really just condescending. The sooner you realize these things about yourself, the sooner you can work to change that and have a chance of actually having someone like me listen to you. For now, I'm going away."
Why these are things I wish I could say to people and can't is that I *know* that no one wants to listen, so I just cut to the going away part myself. More peace that way.