You can hide people from your Facebook News Feed, but that won't stop Facebook from popping up elsewhere, constantly recommending that you view photos of your ex and his/her new flame. Here's how to completely hide someone from Facebook.
When Facebook first implemented some of its new recommendation features, a lot of people found their ex's photo albums, profiles and other updates ended up in that sidebar more often than not. This makes sense, since for a while they were probably your most contacted Facebook friend—but after a breakup, it isn't exactly what you want to see on every page. Facebook's since edited these photo boxes to avoid exes, but it only works if you were listed as in a relationship with that person on Facebook—so it doesn't help if you want to completely hide the secret exes, random hookups, or people that just bug the hell out of you.
Google Chrome extension Eternal Sunshine hides anyone you choose from nearly every corner of Facebook, including your news feed, profile updates, photo updates, suggested photo albums, and Facebook Chat (both the list and mosaic). It's a nice way to keep them out of your face without outright unfriending or blocking them. You'll still be able to visit their profile if you search for them, which is nice—after all, you still need to know how crappy their life is without you—Facebook just won't be dangling their profile in front of your face all the time.
Just hit the link below to install the Chrome extension, then visit the profile of the person you want to hide. Grab their username or user ID number from the URL of their profile page (it will only display one or the other), and paste it into Eternal Sunshine. Once you hit Enter, the extension will start hiding them from Facebook.
It isn't quite perfect; I've still run into one or two instances of hidden friends while I was testing it, but jarring ex updates showed up far less often than it had before. And, of course, you're still going to see all their comments or tagged photos if they appear in your friends' albums. If you want to truly remove every trace of them, you'll have to block them, but this is a good way to keep them out of your way without starting any drama ("I thought we were going to handle this maturely. Why did you unfriend me?"). Plus, it's quite a bit better than Facebook's built-in "Hide" option. Give it a shot if you can think of a few people you'd like to see less of.
Eternal Sunshine is a free download, works wherever Google Chrome does.
Eternal Sunshine [Google Chrome Extensions]