I have theory regarding the word "hilarious". I am not completely, unshakeably sure if this is a generally applicable theory, but I am at about 98%. My theory is that when used on the Internet (the web, social media, chat rooms, etc.) the word does not mean "extremely amusing" as it does in the dictionary; it actually means something closer to "a lame or forced attempt at humor resulting in something that makes you click away and scrunch up your face in a perplexed manner".
I am quite serious about this, and I am not an old grump. Well, I can be an old grump, but I also do still have an actual sense of humor - I mean, I have actually laughed out loud while reading The Hitchhiker's Guide To The Galaxy. And I don't mean I LOL'd - I mean I actually went "Haha! Chuckle, chuckle, snort!" out loud.
I encourage you, dear reader, to test this for yourself. Look for a blog post, Facebook or Twitter item etc, where they insist that such and such is hilarious. I can almost guaran-damn-tee you that it's not. I have noticed this for some time, and while some sites are more prone to this that others (Yahoo!, MSN, I am looking at you), they all do it to some degree.
Here is an example to get you started (which is described in the article as "completely hilarious", so they really went for it with this one).