Where's the fine line between ignoring and getting angry, lecturing and stronger consequences? If this is 10, what's it going to be like in five years?
Answer: Possibly much better. There are times as all kids grow up when they need to separate themselves from their parents, be it physically, emotionally, politically, whatever. It's part of their essential process of building their own identity. They do this hard work internally at every point in their childhood, but at times it's low-key and other times the internal struggle is so great it sucks the whole family in.
It's quite possible you're in one of those phases now, and it's exacerbated by his being a twin. He might not be willing to rattle his connection to his twin, so he rattles yours all the harder.
You might consider talking to the counselor at your kids' school, just to ask about 10-year-old-appropriate strategies and also about good books on the subject.
If you find yourself losing your stay-calm resolve more or if the situation escalates, ask for referrals to a family therapist whom you can call upon more regularly. It doesn't need to be a long commitment; after getting to know you both, a good problem-solving pro can bring light and ideas in a session or two.
Email Carolyn Hax at email@example.com, or chat with her online at noon Eastern time each Friday at www.washingtonpost.com.