a "Dear John" letter is a term for a letter a woman writes to man ending their relationship. (I'm not sure why it's called that, and you don't hear it very often anymore!) ie "She sent him a Dear John letter while he was in Belgium, but there was a mix-up in the post and it never arrived." "leave me hanging" is kind of slang between guys. It's kind of dumb so I'll let urban dictionary define it. 1. leave me hanging 112 up, 20 down Originating from high-fives. It's considered rude to not return a high-five when someone puts their hand in the air—there's no graceful way for them to lower it without someone returning their high-five. Their hand is left hanging in the air. So, whenever a person leaves another person in a situation where the first person is waiting for a response--and not getting it from the second person--it's referred to as being left hanging. "Yo, dude, don't leave me hanging!" http://www.urbandictionary.com/define.php?term=leave%20me%20hanging