This story is for you if...
1. You chicken wing.
2. You don't know if your elbow is bent or not, but something's definitely not right.
The Fault
You chicken-wing. You can't really see yourself doing it because it's happening at the fastest part of your swing—impact—but that bent left elbow in your follow-through is easily diagnosed by the never-ending series of slices and thins you hit with every club in your bag. When most golfers attempt to fix their chicken wing, they go right to the source: their left elbow. Yes, that's part of the problem, but the main culprit is your body turn, or lack thereof. When your trunk stops rotating at the bottom of your downswing, the clubhead passes your hands and causes your elbow to bend.
The Fix
Here's a drill that will help you maintain your turn from the ball and keep your left elbow from folding up. Grab your driver with your left hand only and set the back of your right hand behind your left elbow. Make an easy swing with your left arm back and through, applying pressure to your left elbow the whole way. You should feel a strange sensation as you swing through impact: your left elbow turning down—not folding up—and pulling your upper body into the shot, which forces you to turn all the way through. Goodbye, chicken wing, hello power.
Swing back and through a few times with your right hand behind your left elbow to help groove the feel, then take it to the course. It's not a bad idea to perform this drill just prior to teeing off to remind yourself to continue your pivot through impact and keep your chicken wing in the coop.