response given when someone is obvioulsy confused or completely 180 degrees from accepted fact/reality; can also be used to keep one's ego in check
Jim: Dude, that hot chick walking over here is checking me out hard!
Steve: Um, these aren't the droids you're looking for. That's my girlfriend, dude. She just came to drop off my car keys. Move along!
the nicer way of telling somebody they suck at something that they have just started to do. translates into "you suck, but since you're a beginner it's okay."