Facebook may connect millions of its users to each other with its messenger service, but it can also make it very difficult to avoid those annoying "friends."
The problem is, when you use the default Facebook Messenger app, you get the added bonus of a timestamp added to messages that you have seen. Instead of being able to view and ignore an incoming message, the other party will know that you've seen it and are actively ignoring them.
To spare them the heartache of seeing your disinterest, and yourself any awkwardness associated with that, use Seen At..?? for Facebook by devs Mannaia. This two-man team created the app to get rid of the pesky timestamps for themselves, and decided to release it for free to the masses.
Seen At..?? for Facebook is free on the Google Play Store, and requires no special permissions to get set up.
After installation, sign in to your Facebook account and...that's it. The app won't import your old messages, but from now on you can use it to view all of the messages you don't want those certain people to know you've seen. Check out the screenshots below if you still need some convincing.
Maybe with this new found power, you can finally get those annoying friends to leave you the hell alone, at least until you get around to deleting them with all of your other inadequate "friends."