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.)