Answer:
Well, let's say you're out at a bar. A friend of yours sees a cute guy, but she's hesitant to make the first move because she assumes the guy would be turned off by that - because we're socialized to believe that women shouldn't approach men like that, lest they come off as desperate. That's heteronormativity.
When she finally gets the courage to go up and talk to him, he begins to call her infantilizing pet names (like honey, baby, and sweetheart) - which would be fine if they'd agreed upon it, but he's just assuming she's cool with it! That's heteronormativity.
When she begins to get uncomfortable by these names, she gets up and leaves. But the guy says something like, "Oh, come on! Women are so sensitive. What's your problem?" That's heteronormativity.