Please state what country your phrase tends to be used, what the phrase is, and what it should be.
Example:
In America, recently came across “back-petal”, instead of back-pedal. Also, still hearing “for all intensive purposes” instead of “for all intents and purposes”.
Well if we’re going to be talking about logical fallacies, I feel like the string of arguments that you made there is a category error. Infinity isn’t exactly a number, it’s more of a philosophical concept than anything else. I would argue that trying to subtract Infinity from Infinity is illogical and kind of silly, but it wouldn’t be a reductio ad absurdum as you put it, but instead a category error.
An absurdist argument might be more like, if I have one cat I can trade it for one dog. Therefore infinite cats can be traded for infinite dogs. This is obviously absurd, because infinite cats don’t exist, unfortunately.