An Impassioned — But Likely Hopeless — Plea

It's spelt/pronounced geniuses, people.  G-E-N-I-U-S-E-S.  The only permissible time at which you should pluralise it as genii is if you're using it in the slightly archaic meaning of "(in some mythologies) a spirit associated with a person, place, or institution"¹ — from which we get the word genie.

"But I was told that in Latin you could pluralise words ending in -us by replacing it with an -i."  That would be fine — if you were using Latin.  (And, if you were, you'd only be using the word in its spirit meaning.)  You are not using Latin, you are using English, and in English genii and geniuses have different meanings.  (Seriously, this -i business is getting out of hand.  Virii?  That would be nice, except that the Latin word viri is actually the plural of vir, meaning men.²  So, if you're saying virii, what you're actually saying is grammatically incorrect Latin whose closest English equivalent would possibly be mens.  In fact, about the only -i ending English plural that won't send me searching for a dictionary to smash you over the head with is octopi, if only because it's fairly well established (as in: decades, possibly longer); however even that is technically incorrect: octopus is actually Greek in origin, meaning that the grammatically correct plural using the word's language of origin is actually octopodes³.)

So, let's review: multiple highly intelligent people?  Geniuses.  Multiple supernatural beings?  Genii or genies.

1. Compact Oxford English Dictionary entry: genius
2. University of Notre Dame Latin Dictionary and Grammar Aid, vir stem + i ending
3. Compact Oxford English Dictionary entry: octopus