Granted, a guy could get this piercing, too, but to be honest its attraction lies in bringing attention to the female cleavage. A flat chest really wouldn't showcase this piercing the way it was intended, because there would be too much empty space on either side of it; it would look like a floating piercing on your chest that was placed with little intention.
As attractive as it may be, this is a high-risk piercing as far as rejection rates go. It needs to be pierced by someone who's highly skilled in doing surface piercings, and it's essential that the correct jewelry be used. A flexible rod or surface bar are your best options, and titanium seems to be the most "implant friendly" metal if you're getting a surface bar. After that, the way you move, the way you sleep, and how you take care of your piercing will all play a major role in how good of a chance your piercing has at healing. But even if you do everything right, there's a good chance that your Cleavage piercing will be temporary. If you want it for a special event, have it done about a week before the event - just in case.