If you use Facebook, you've almost certainly noticed the ads on the right-hand side of most pages. And chances are you've also noticed the little "x" in the upper right-hand corner of each ad.
It's the "I don't like this" link (the opposite of that little thumbs-up icon under each ad), and I use it regularly. I let most Facebook ads slide, but some either offend me (usually with a gratuitously sexist photo, or a clearly misleading come-on) or are just so clearly not intended for me (thanks, but I'm not in the market for a condo) that I end up clicking - more to alert Facebook than for any other reason.