I just saw a TV commercial with a very beautiful woman in her underwear saying "how do you know when you're wearing a really good bra?". She was about a 34 B and had no need for a bra--never mind a good one!
So here's how you can tell:
1. It cost more than the sum total of everything else you are wearing. Including your jewelry and whatever your parents paid for orthodonture.
2. It hurts a little.
3. It only comes in beige. And the 5 foot tall sales lady with the tape measure around her neck looks at you like you have 10 heads when you ask if it comes in red. And you realize just how easy it would be to strangle her with that damn tape measure.
4. Your left boob is no longer under your right arm.
5. You paid a surcharge to the Ironworkers Union for crafting the underwire. Which you know is going to pop out at the most inopportune moment. Which was funny--once.
6. It doubles as a catapult. (I was going to say slingshot but honesty is the best policy. Slingshot implies that it would fit in my pocket.)
7. It doesn't fold in half.
8. It was designed by McGuyver.
9. When you put it on, you find that number 2 double point that you stuck under your right boob so you wouldn't lose it while you were turning a heel. And then forgot where you put it. (Let's not talk about the good scissors.)
10. People stop staring (and pointing and laughing).
11. It has the ability to unbalance your washer and make it thump across the basement floor when it is in there by itself.
12. When you put it on, you don't have to manually line up your nipples (which you do have to do with a bad bra).
13. It has it's own alphabet. There is no double D in the alphabet song.
14. If you fall asleep in it, you dream about boa constrictors--and not in a good way.
15. When you unhook it your entire body shivers with relief.
I've decided that boobs are like corn on the cob. They're really great for a very short window of time.