On Facebook its easy. On any post, just click the x on the right hand side and choose if you want to hide just that one post or all posts from that person. If you change your mind (and lets face, don't we all from time to time?) just go to the drop down settings beside Most Recent at the top of your feed, and the list of your hidden pages and friends are all shown there.
This means you don't have to unfriend your friend and then refriend them if you have a bit of tiff. In fact, they wont know at all that you've hidden them - perfect.
Likewise LinkedIn has a similar feature. Bless. Although you can only hide all updates from a connection, not a single update.
Over on Twitter though, things are not so easy. You can unfollow someone which will stop their tweets from appearing in your stream, however they can still mention you (but not DM you). They may also notice that you have unfollowed them, so be prepared for that conversation. Or you can block them but that may be too extreme. You also can't filter out a hashtag or tweets with specific words - so you are forced to endure it in exasperation or abandon Twitter completely for a while.
And you can clear the filter when you want to.
So easy! Try it and enjoy the peace that it brings.