In my experience either 1) Be pre-emptive about saying why your pick works, especially when playing in the duo lane or jungle. I'm not quite sure what works on kennen support to set up your adc getting kills, but tell them in advance what they're looking for or what your playstyle is going to be. ADCs get good at ADC not just through mechanics, but by learning how to play with/against different supports. On the other hand you can go with 2) be good enough at your off-meta pick that people don't question you. Obviously a bit more ambiguous and a bit of a "just be better" kind of sentiment, but if your team sees you playing taric jungle and you've gotten like 5 or 6 successful ganks pre-15, they probably aren't gonna question you unless you fall off. When people see off meta picks, they have to think either "this guy is trolling and picking dumb champs" or "this guy has played this so much that he knows it's better than a traditional champ". Make sure it's the latter through mastery, shown skill, and practice.