Literally stands for "Kiss me you fool".
Usually references a movie scene in which two characters are at the dramatic emotional moment just before they fall into each other's arms and declare their undying love for one another.
Can also be used as sarcastic humor to comment on overdone emotional intensity between two obviously non-romantic characters.
"An emotional argument revealing long hidden feelings, ended with a long simmering stare-down? Well if that's not a KMYF moment I don't know what is."
"What?! They're brothers for crying out loud."
"And if this movie had a higher rating they'd be in each other's arms by now."