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..."