No matter which brand you buy, microwave popcorn never tastes as good as its movie theater counterpart. Even if you pop it yourself on the stovetop and drizzle it with real butter, it doesn't have the same flavor. That's because movie theaters don't use real butter—their popcorn has one secret ingredient that gives it that distinct taste.
Flavacol is a super fine, butter-flavored seasoning salt that movie theaters on their popcorn. They usually pop it using a combination of orange-colored coconut oil and Flavacol seasoning, but regular coconut oil will give you the same results without the fake-looking color. Other good coconut oil substitutes are corn and palm oil.
You can buy Flavacol from Amazon for about $6, and a little goes a long way. Redditor datoneazn bought a four-quart package that he's been using for years—you only need about ¾ teaspoon for each ½ cup of popcorn kernels. Just sprinkle it on before you pop the kernels.
If you're worried about the possibility of diacetyl fumes, which are only an issue when heating it up bulk quantities, simply sprinkle on the Flavacol after you pop it in oil instead of using it while you pop it.
In addition to Flavacol, datoneazn says that steam is the other key component to making the best popcorn ever. When you pop it on the stovetop, leave a lid on the whole time so the steam all stays in and keeps it from getting dry. Check out the reddit thread for more tips.