Octopi, octopuses, and octopods are all valid pluralizations of octopus in American English.

Conversely, cacti is the only valid pluralization of cactus.

Don’t worry, language itself pissed us off long before you did.

octopiussi

Linguists are probably the least likely people to get upset at someone using the “wrong” word. they might pull out their notebook and start asking you questions though