"Science doesn't have all the answers either!"

 

"Well, your system of morality isn't perfect!"

 

This is when the opponent deflects criticism of their argument towards you instead, saying, "You too!" The problem with this is that they have not addressed the criticism of their argument at all. They are trying to get around it by implying that your position has similar problems, and so is not superior. 

It may be the case that your position has problems, but that is irrelevant when discussing their position. That is a separate discussion. Of course, your position may not have such problems, in which case it is just a cheap deflecting tactic to cover the weakness of their position.