How do you know when you’ve crossed the line from standing up for something you know is correct and acting like a smart ass?

Am I to sit back and allow others to ‘dumb me down’ just because I know better than them about a certain subject, and they can’t stand to hear the truth and facts? I mean, I know that people feel as if they’re right all the time. We as a human society don’t like to be wrong, but honestly, if I didn’t know something I would admit it. Conversely when I do know, I feel like it’d benefit others if they knew too (only if the conversation permits such information to be introduced though of course). Is it not my business to correct the inaccuracy of others? Is keeping my mouth shut while sitting there listening to a conversation with full awareness that the other guy has nooo idea what he’s talking about, the only true and valiant behavior for these situations?

Really, can I get some opinions here? I keep saying that I don’t enjoy the company of know-it-alls, but after being called one myself this evening, I’m ready to reevaluate my personality so I do not end up being that which I have lobbied to dislike.