I think we have established that that is in AMERICAN English. English as used in other circles can be quite different. That's what makes something jargon. It's language that seems familiar to the people in your usual circle, but might be incomprehensible, or have different meaning entirely, to someone outside of that circle. It is, therefore, the language of elitism and exclusion.
At this point you aren't even describing jargon but have somehow shifted into complaining about differences in vocabulary between dialects whilst still calling it "jargon". Which, seeing as you're from the United Kingdom of Great Britain and Northern Ireland, makes your complaints about supposed "elitism"
extremely hard to take seriously, given that the English practically
invented elitism. Small consolation for me that the sun finally sets on you all. And even then, forgive me if I'm skeptical of the claim that the term ad hominem is incomprehensible and completely foreign to any of the 40-odd dialects of British English.
I have two cousins from Singapore. Their standard English is pretty good, as is their Mandarin, so we can communicate with each other without much issue; but they also speak the local creole, Singlish, which is largely English based but incorporates words from Malay, Mandarin, and Hokkien. When they talk in Singlish, they become completely incomprehensible to my Canadian ears. But for me to accuse them of using the vocabulary and syntax of their native language as "elitist" would be both culturally insensitive and just plain ridiculous.
And you haven't established what makes it a fallacy - i.e. not true. I can see what makes an attack against the person wrong, but that is not the same as false. And that wrongness rather fades when the person is long dead.
Do you call it a fallacy simply because you have been taught to call it a fallacy at school?
A note: fallacies are not "false statements". They are specifically examples of errors in reasoning and logic that render rhetorical statements unpersuasive. Their truth value is independent of their poor construction as arguments, the latter of which is why they are classified as fallacies.
With that in mind, argumentum ad hominem is a subset of the fallacy of irrelevance, an argument that has nothing to do with the topic at hand, failing to refute the opposing argument by completely missing the point. Unlike a formal fallacy, a statement which is fallacious because the internal logic of the statement does not follow rendering the whole statement non sequitur, ad hominem is a type of informal fallacy, which are errors in reasoning rather than logic; the statement is logically consistent, but it mishandles or even ignores the content of the debate, and thus is unpersuasive. An ad hominem statement is fallacious, despite being logically consistent with itself, because it does not refute the opposing argument but instead serves to divert and mislead the audience's attention by attacking the opponent's character, creating the perception that the contents of the opposing argument are erroneous due to their association with the opponent's character, despite never actually refuting the argument itself.