A cup of popcorn has only 3 net carbs. Two problems, though:

1. No mere mortal can stop at just 1 cup of popcorn. Even the smallest size they sell at the theater is probably 10 cups or more.

2. Popcorn is relatively high on the glycemic index, which means it'll spike your blood sugar. It's like eating "just a little bit" of rice or real sugar — carb count is not all that matters.