“What’s that sound coming from beneath the floorboards?”
“Oh, that’s just my ringtone.”
“Octopi” is shorter and easier to say than “octopodes” and it’s consistent with most other loan words in English that end in -us. Who cares if it’s not correct Ancient Greek? We’re not speaking Ancient Greek, we’re speaking English. Substituting a second-declension Latin ending for a third-declension Greek ending is the least of this language’s problems.
Anyway, I think we all know that the correct plural of “octopus” is “hentai.”