To understand a kid and get them to understand you, you need to know the lingo. And I don't mean the hip new words they make up so they think parents can't understand them. Please, like that hasn't been going on for centuries. Maybe we should start talking like we did as teenagers and they won't be able to understand us. I can see it now, I will tell dh our son is dirty, "Dudes grungy." Son will be totally oblivious to the fact he is about to be sent for a shower.
Anyway, you need to speak like they do to get them to do what you want. For instance if you are arguing with your son that he needs to shower and he claims he showered last night this is how you win the argument. "Well then if you showered last night how come you didn't complain when I told you last night that you have to shower in the morning?" His response: "I forget easily." So I say, "Well if you couldn't remember last night that you showered last night, how can you remember today that you showered yesterday?" Not sure if I totally confused him or won the argument but he walked away. I am counting it as a win for me. But only if he showers.