(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!
when something is so hilarious it needs to be changed to the plural of hilarii. pronounced hilari-eye
do you remember when johnny found out he was kissing a guy. that was hilarii