In reply to K ) who wrote this in
, I, Marvo, say :

Uncle Marvo writes
In reply to Mike ) who wrote this in
, I, Marvo, say :

is it penises or penie ?

Any experts in grammar/english/plurals here?

Well, I've spoken it reasonably well for 50 years, apparently.

It is clearly penises. It isn't latin, if it was it would be penius,
and the plural would be penii.

Why would it be 'penius'? There are plenty of latin words ending in
'is', eg civis, and the plural would be 'penes'. cf Analysis/analyses.
Browsing the OED suggests a lot of the latin -is endings are words
they got from the greek.

I forgot the :-) at the end of the post

:-)