Sometimes, you might have a certain someone who gets a little, shall we say, overzealous in trying to message you. Since your iPhone and Mac can both receive iMessages, you might get interrupted by the flurry of messages from this certain contact.
While you can block iMessage senders on your iPhone or iPad, it hasn’t been possible in Mac OS X Mavericks until the latest update to 10.9.2, available through the Software Update panel of the Mac App Store.
Now, though, you can block and unblock any contact in your Contacts app with aplomb, right from your Mac.