If someone makes a joke about it in conversation, I'll laugh, but I'd ghost the group in the first session if I go to the GM's place and see a copy of it on his/her bookshelf.
That's a "magical realm" I want to stay far away from.
From what I heard about it, it wouldn't even be fun for the meme. It's too complicated to play for a laugh and too insane and twisted to play seriously.
In 2023? I don't think so. I got into D&D decades ago and THAC0 was already not a thing anymore. Gurps may not be widely played today but I still see it getting memed a lot for being complicated.
GURPS is such a great system. A lot of rules, but they all make sense, and it's so flexible.
THAC0 (To Hit Armor Class 0) was an attempt to simplify combat in earlier editions. Before then, each class had a table they had to refer to to know what they had to roll to hit a particular armor class. It's much simpler in 5e.
In addition to other great information here about THACO, it's worth highlighting that it was upside-down.
Lower rolls were better.
This led to magic items giving both pluses and (good) minuses in order to remain consistent in world. Also some curses and ailments gave (bad) pluses to certain rolls.
Casus Belli as in a reason to declare war or something else entirely? Because if that's it, all Stellaris and Paradox Grand Strategy Games Player know about that one. Or history enthusiasts.
Yo what about the gurps/carwars crossover combining two of the best games ever to hit print? Also no love for HōL and the cover of the second printing of their expansion book BUTTery HōLsomeness that was such a pita for me to find that I questioned if it even had a physical printing and took years to find the damn thing?
One of my favorite weirdly specific rules is from Dragon Magazine #10. Where it gives rules for being in an orgy for as many days as you have con points, so most characters can get it on for like 2 weeks straight lol:
Orgies. Fighting Men (excluding Rangers and Paladins), Bards,
Thieves, and all Chaotics (excluding Monks). Lusty indulgence in wine,
women, and song. Maximum expenditure is 500 GP per level per night
(250 GP if recuperating and under 50%). A player may orgy continuously
as many days as he has constitution points, but then must rest
for as many days as he orgied. (For effects on Psionic Powers, see Appendix
II.)
Makes me feel sad my favorite system isn't well known enough to be here (HERO system, or champions), but it always warms the heart to make fun of old White Wolf stuff some more