A Science Stopper is " a hypothesis that makes no testable or useful predictions and therefore prevents any science from being performed based on that hypothesis." A common example of this would be the claim that God(s) created our universe. Having no way of telling "created" universes apart from "non-created" universes prevents the claim from ever being verified or from being debunked.
When he theoretical physicist Wolfgang Pauli was presented with untestable hypothesis by his students he would use the phrase, "It's not only not right - it's not even wrong." When you make a prediction and that claim is shown to be right or shown to be wrong there is an increase in knowledge. However, when the claim cannot be tested there is noting gained. It's just an empty ad hoc. While these sorts of things make for great premises for a movie plot (e.g. The Matrix) they sever no function for making determinations about reality.
When someone says 'you're not even wrong' it implies that "not only are you not making a valid point in a discussion, but you don't even understand the nature of the discussion itself , or the things that need to be understood in order to participate."