'Myther it, tell them float', 'You're mythering, tell them float', or simply 'tell them float' is an expression used to tell people that what they're saying/doing/feeling is not that deep and they should simply deal with it.
The expression comes from if someone was drowning or struggling to stay in water, you would tell them to float. In this idiom, the water that they're drowning in is the situation that they are taking too seriously; and they should simply float above their problems. Not solving the problems, merely floating above them.
It's important to note that the person facing these issues are told to themselves "Tell em float". Almost as if the peer to peer conversation is actually a group bullying whereas the person telling them to float is calling for people to back him up.
"I really hate how hot it is in here"
"You're mythering, tell them float"
"I cant stand the way she dresses"
"Float, its not that deep"
"I cant pay my bills this month"
"Tell em float"