At Imperial there was the "asssassins guild", the idea being that each term members would be assigned the name of someone they had to "kill", preferably in quite an elaborate way. But I don't think it's been active for at least a few years.
There are some other very niche societies, like Renal and Urology. Kinky Klub is the one that all the freshers discover and join for a laugh, but the person who was really leading it the past few years has graduated and there's no committee for it anymore.