In violent agreement with Nathan Wheeler's answer, I'll just word things a bit differently. "man-boobs" are fat. I had them, and when I was heavier they even hung a little bit. Not flattering at all.
Unfortunately, there is no way to target weight loss to any given area of your body. The only thing you can do is lose fat all over, and the man-boob and keg abs (my problem area) will go away. The best way to deal with fat is through diet.
Now, if you want something impressive when the fat is gone, you need to strengthen the muscles underneath the fat. Muscle groups can be targeted, and bench presses are an excellent way to improve your chest.
As to how my man-boobs have melted away (still a bit in progress):
- If they were sagging, they stop
- The whole chest will look larger, not quite firm pecs yet, but a lot more impressive than they used to be
- The chest will appear to get smaller again, but as the fat gets burned off it leaves behind the muscle
- Now they look like pecs. They aren't massive, but they'll improve over time as the muscle gets stronger.
The same will happen with my keg abs. My "dunlap" disease is gone (where your belly "done lapped" over your belt), and the core below the belt line is tight and right. Unfortunately, above the belt line I have this bump of fat--slowly but surely shrinking. Eventually it will start looking like abs, but for my body it's the last place my fat is holding on. I really wish it was possible to target weight loss, but the best I can do is leave something strong for when the fat is burned off.