1. Something so funny it makes you feel like you've just dropped
acid and got high on ecstasy at the same
time.
Or:
2. Something so unfunny/
dumb that you must be literally doped out of your mind to derpidly laugh at it.
Sober
friend:"Dude, did you see what Dumbnuts just did? HiiiIIIIGH-larious!"
or, alternative usage:
Trashed
friend: "BwahhahahahaHAhurdeehuehurheeehehehehaHAr, that is sooooooo FUuuuurrrnyyyheeheeehehehheeee *hic* lolololol"
Unamused sober
friend sarcastically responds with mocking tone: "Haha, yes, very funny, Highlarious..."