Edit: Nice to see it was fixed. Anyway, to anyone who can't read Japanese, the basic premise seems to be this:
Some guys managed to "defeat" Shampoo through the use of a Taser gun (since she was defeated by males, she has to marry them according to the setting from the manga). Ranma is dragged into the affair and he/she sees Shampoo enjoying herself to the guys to which the guy explains that they found a "Jewel of Reversal" which changes hate to love and love to hate (depending on how it is worn). They put it on Ranma (in the way that love would turn to hate) and he/she ends up showing hate towards Shampoo (which means he/she likes Shampoo) but then after Ranma's climax, Ranma says he/she likes Shampoo (meaning that Ranma's attitude towards Shampoo probably changed somehow [into hate, possibly]). Shampoo realizes this and ends up shocked and just goes along with it thinking that even if it's a fake love, she's still together with Ranma.
averagejoe32: I'm not quite sure where the Yakuza comes into it, really. It's been a looong time since I've read anything of Ranma so it might be from a storyline or it might just be a device that Kyoten Heichou used for this story (since it's easy to characterize Yakuza as the type of people to do things like rape and such). And it does look like you're correct that Ranma has been subjected to the "Legendary Moxibustion of Evil")
By the way shinyuu if you can read Japanese where does the Yakuza come into it as you can the can fucking Ranma seems to have Yakuza tatoos (check out page seven), furthermore if you look on page 14 and 5 you can clearly see Ranma has be subjected to the ultimate weakness moxibustion again, check it out in the trivia section here - http://ranma.wikia.com/wiki/The_Legendary_Moxibustion_of_Evil#Trivia