Shows irritation with someone's actions or words, more emphatic than just saying 'stop' or 'enough'. For crying out loud, can't you see I'm on the phone?
Pro Tip 2/3
Emotional Intensity
Adds drama to a statement, making it clear you have strong feelings about the situation. I've told you, for crying out loud, that's not how it works!
Pro Tip 3/3
Not Literally Crying
The phrase doesn't mean someone is actually crying; it's just a way to emphasize frustration. For crying out loud, I left my keys in the car again!