It originated in Prague due to two incidents:

* https://en.wikipedia.org/wiki/Defenestration#Origin

* https://en.wikipedia.org/wiki/Defenestrations_of_Prague

Also used in Italian and presumably in many other languages.

Like with any word, it's use in colloquial form may vary from generation to generation, from subculture to subculture etc

Not at all. It's just the Latin prefix "de" (out of) plus "fenester" meaning window. Not an English word except by borrowing.

The joke was that [to my then knowledge] it's not used in Romance languages, but it is used in English.

I believe the term originates with this historical event:

https://en.wikipedia.org/wiki/Defenestrations_of_Prague

And if you believe Wiki, it was used originally in Middle French.

Is it? I know of that word in at least 3 languages.