The answer is nobody can give you a definitive answer. That said, common sense says to me, do it once and nothing is going to happen. Make a habit of it and it might draw some attention, but what business is going to take harsh, arbitrary action without some sort of warning...do we really think they're going to have the Soup Nazi from Seinfeld call you and scream "NO FLIGHTS FOR YOU!!!!!!!!!!"?

As one of the other posters noted, plans change, things happen...maybe you caught COVID on the flight to NYC and were too sick (or too responsible) to take the onward leg...any number of reasonable excuses and I don't think there's a large sample where people have reported been harshly punished for doing what you suggest. (well there is that kid on American that got flagged for skiplagging, but he TOLD them at check-in what he was doing so likely a few sandwiches short of a picnic there..)

IMHO airlines in general, and AC for sure, do lots of things that I think are un-ethical or exercise business practices that encourage this kind of behaviour, so I'm not really crying in my beer for them...might actually work out to their advantage if they oversold your flight and they can put a fresh revenue bum in that seat when you no-show...none of the 'we all must follow the rules and adhere to the T's&C's never seem to bring that little nugget out.

Please let us know how it goes!