A negative response to a statement. This answer first acknowledges that he/she understands what the other party is saying but ultimately he/she disagrees. Its a firm hard-no type of response delivered with a diplomatic spin.
It typically precedes some sort of follow up statement that might provide some perspective on why the answer is no, or it may simply be an insult.
"Yeh nah. You're an idiot."
"Yeh nah. Futurama was in no way better than the Simpsons."
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"