Tu Quoque is when you dismiss someone's criticism by saying that the criticizer has the same flaw. Everyone thinks it's a fallacy, but it's often not. The examples that people give for it are usually ones where the criticizer acknowledges that they have the same flaw (eg. me talking about how the purpose of life is to be a perfect person while I spend hours every day playing video games and browsing memes on reddit). In these cases it's a fallacy. But if I were to say all that without acknowledging my hypocrisy, that would indeed be unfair and people would have the right to dismiss my arguments. It makes no sense to say that my opponents have to deal with my arguments validly while I don't. I don't get a free pass just because I shot first.