(Pronounced: Hilari-eye)When something is so humourous or hilarious it has to be changed into the plural form.
Evan:Dude, Paul got attacked by a shark!
Alex:Thats hilarii!!!
Alex:Aliens have landed and they're 50 foot vikings trying to kill us all!
Evan:That isn't hilarii!
Alex:Thats hilarii!!!
Alex:Aliens have landed and they're 50 foot vikings trying to kill us all!
Evan:That isn't hilarii!
by Alex Cardenas November 19, 2007
by adamisaspaz March 06, 2003
when something is so hilarious it needs to be changed to the plural of hilarii. pronounced hilari-eye
by Sheehan boi November 03, 2011