Hilarious, derived from the Latin hilarus, has been well known to English speakers since around 1840, but totally lost its shit after dropping acid at Burning Man back in 2007. When it finally managed to extricate itself from the overflowing portable toilet that had become its temporary home and piece the fragments of its shattered psyche together, it was hilar. Deployed nearly every time a teenager becomes mildly excited, its popularity in the Twitterverse is such that it is often used inaccurately – e.g. to describe the comedies of Jennifer Aniston.
“LOLOCAUST. The ‘Gangnam Style’ video is totes hilar!”