A word made up by people uneducated in the ways of etymology. NOT THE PLURAL OF PENIS.
The rule with aplural form with an I is derived from latin and is only applicable when the word ends in -US, and has no relevance whatsoever when the word ends in -IS.
When a word ends in -IS, the correct plural form is, in fact, -ISES.
(US-I)
The Octopus was languid.
The Octopi were languid.
The radius was 5cm long.
The radii were both of the same length.
The Hippopotamus was huge.
All the hippopotami were huge.
(IS-ISES)
Within most species the penis is used for reproduction.
The correct plural or penis is penises, not penii.
Pronounced {Peen-I}
A Small, Mostly Hairless Animal That Lives Anywhere Men Are, And Sometimes Where Women Do. Penii Are Usually Very Slow Creatures, Unless Presented With An Opertunity Of Sorts. They Can Hunt At Anytime Of the Day Or Night, Their Prey Being The Vagii. They Commonly Travel In Flocks.
A Flock Of Penii Just Passed Us, And I Think They Shat!
Kid 1: Dude, he just drew a bunch of penii!
Kid 2: What the hell is “Penii?”
Kid 1: Its the plural form of penis. Duh
Kid 2: The plural word is Penises. Idiot!