Can I have a raviolo on the side? and a biscotto for dessert?
I actually do occasionally ask for “a chocolate biscotto” when I get coffee, just for kicks.
This thread is the first time I’ve ever heard that “cannon” is the plural for “cannon”.
I don’t have a subscription to the OED ($100 a year for what would be fairly limited use is a bit steep for me), but I did find this reference:
Shelley Berman had a routine on irregular plurals back in 1959.
“I just want to say just a few words about stewardii. They have… (he is interrupted by crowd shriek of laughter) Stewardii is plural for Stewardess. Uh…I think there are many incongruities in the English language as far as plurals are concerned. For example, it seems to me that the plural for Yo-yo should be Yo-yi. How about, one sheriff; several sheriffim. Um…one goof; a group of geef; uh…one Kleenex, several Kleenices; one Blouse, two Blice …Two Jackii.”
Here
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED6678
you may find quotations about canons, canonys, kanonys, and canones.
Richard Lederer has an irregular plural article:
And, of course, there is Brian Regan’s bit about pluralization:
Are you referring to the difficulty that speakers of Romance languages often have with “his” and “her” in English -in Italian/Spanish/French , the possessive pronoun matches the gender of the object that is possessed, while in English , the gender matches the person who possesses it. There isn’t a one-to-one translation for “his” and “her” - in Italian “suo libro” might mean either “her book” or “his book”.
These jokes miss the point that (at least if you know something about Germanic languages, which I do not and the joke-teller is missing the opportunity to educate us) that “mouse” is a strong noun with a consonant stem, therefore “mice”, while the plural of “house”, in Old English anyway, would be just “house”. (cf modern German Mäuse/Häuser)—also houses are neuter while mice are feminine.
ETA Wikipedia gives proto-Germanic hūsą/hūsō, mūs/mūsiz)
Wait! I thought the singular was chupacabra and the plural was chupacabrae.
Has anybody decided that a single grain of maize is a may?
That could be it. Kinda funny that they can easily remember to choose between il(s) and elle(s) but might be stumped by his and her.
It is, but that spelling is incorrect. It’s chupacabræ. When you have a very large group they become chupacabræs 
.
Who shouldn’t be confused with chupaca-bros!
You can shoot (a) moose with (a) cannon…
Data is another one. Technically, the singular is “datum” and if you use the word “data”, you should use the plural version of a verb with it - e.g. “the data are suggestive of a decline in whatever due to whatever other factor”. As opposed to a single point, where “the datum suggests an increase in whatever”.
But “data are” just sounds contrived and pretentious, even though it’s correct. I admit I’d tend to say “The data is suggestive…” or whatever.
Might be an Americanism too. Something like a team name in England is treated as a plural, while in the US it’s singular. e.g. “Dallas is going to the Super Bowl” versus “Manchester are going to the World Cup”.
I’ve see some people pluralize “Airbus” as “Airbii”, as if it was a Latin word. Even though it’s a portmanteau of the English words “air” and “bus” and thus should be pluralized like “buses”.
Aside: No Latin word forms its plural with the ending “-ii”.
People sometimes make that mistake based on “radii”, but that’s no exception: The root is “radi-”, the nominative singular suffix is “-us”, and the nominative plural suffix is “-i” (just like any other regular second-declension masculine Latin noun). “Radii” only ends up with two "i"s at the end because one is part of the root. This is only difficult for English-speakers to understand because it makes sense, and we’re not used to language doing that.
If “Airbii” were a Latin plural, then, it would be the plural of “Airbius”, not of “Airbus”.
To that point, I have seen “bus” cheekily pluralized to “bi.”
We’ve all seen that. At least, all of us who’ve been here for a few decades and read the columns.
Not chupacabraei?