Snarkiness

Hi! Our 11-year-old grandson (high-functioning autistic) has gotten fresh/snarky of late, voicing a rude or sarcastic reply that is "over the top." We are trying to think how to deal with this using TSG teaching/principles. Here are our questions: 1) We can use The Power of Calm, but it is hard to do that when we want to be firm and not allow or convey "too high" tolerances 2) We can teach him to disagree appropriately, but, that is not always a fit for this ongoing communication pattern 3)same thing goes for "dropping the subject;" while we can use that terminology, it doesn't always fit if we have not – for example – told him to accept a no answer, accept consequences, etc. He IS somewhat in his own world and needs to – in general – wake up to the impact his words and behaviors have on others. We do hold out the "is this how we strive to meet our goal of family unity?" question, but it is not impactful at this time. This behavior seems to be ramping up. Suggestions?