If your teen walks in the door and immediately starts an argument for no reason, he/she may be using the art of deflection. Perhaps teachers have let their students know their grades for the term. So now your teen knows that the B you are expecting them to get in English is now a C, and report cards might be in today's mail. So to preempt the "discussion" about the disappointing grade, your teen might walk in the door with some non-sequitur argument to get the focus off the grade and onto something else less ego deflating.
This happened recently to a parent I talked to. Her daughter walked in the door, and mom innocently said:" Hi honey, how was your day?" Mom expected the usual grunt "it was fine," but instead was bombarded by an avalanche of anger about issues that had nothing to do with school, and that mom thought had been resolved weeks before. Not to mention, this all came out of nowhere! Mom, baffled, got completely hooked into an argument about.......nothing! They both went to bed angry, for no real reason, since the argument was about....nothing.
Next morning, the daughter acting sweet as pie, confesses to her mom that she found out her grades, and they are not as good as she thought they would be. ( the truth is, there is no way she should be surprised) Mom, appreciating her daughter's sweetness and her honesty, congratulates her on being so nice! What happened is that mom was not able to see the dots and couldn't help her daughter connect these two rather disparate emotional presentations.
So when your teen walks in the door and starts up with something, tries to push your buttons and you are left scratching your head. Keep scratching. This should be your clue that something else is going on. Rather than get hooked into an imaginary argument about nothing you might say: " I get you're angry about something, but I don't think it's this. If there is something you need to tell me about, and you're worried about how I will respond, I understand. I promise I will just listen, and not react. I'm here for you, but I won't be drawn into an argument because you are upset, or anxious about something else." At this point, an "I love you" and a "let's talk later," and I think you are done! Real arguments are hard enough, imaginary ones even harder!