Given the XO stipulation that we’re limiting the discussion to wife’s sister and brother’s wife is obviously off limits, it would require a wife that is truly evil and awful to justify it, and no kids can be involved for anyone. That said, it would be literally the greatest spite sex ever, if justified, and also a real life-threatening peak experience since by definition any wife awful enough to deserve to get cucked by her own sister would be fully capable of murdering both of you. So in that 1/100k scenario where you made the mistake of marrying the literal devil it’s not only justified it’s incredibly hot.

(http://www.autoadmit.com/thread.php?thread_id=5610171&forum_id=2PHPSESSID=49d358651cc27ec1964643c2a7b5ece2#48188616)

Scandal is the very foundation of the SIL Fetish

(http://www.autoadmit.com/thread.php?thread_id=5610171&forum_id=2PHPSESSID=49d358651cc27ec1964643c2a7b5ece2#48188745)

It's a combination of many factors. She's a hotter, younger version of your wife (who you were already naturally attracted to--they share the same genes).

She's often proximate to you including during revealing, semi-intimate moments--e.g., lounging around in her robe, changing adjacent to go to the beach, at the pool in her bikini, at a cabin getting dressed in the morning, casually walking into your room while you're getting dressed, asking you to pass her a towel, etc.

The SiL has a natural temptation and desire--this can be conscious or subconscious--to fuck with her sister like all good classic fucked up female relationships and one obvious way to do it is to tempt the sister's husband.

It's a toxic stew that results in you constantly having a throbbing cock around your SiL's pendulous breasts and warm luscious hairy honeypit that she semi-regularly flashes you with even as your rational mind tells you this would be the worst decision you ever made because inevitably it will come back to haunt you and blow up your life.

Thank

(http://www.autoadmit.com/thread.php?thread_id=5610171&forum_id=2PHPSESSID=49d358651cc27ec1964643c2a7b5ece2#48189844)

wife’s bros wife = still deranged but less so

Sister of BIL or SIL not directly related to your wife = fair game except for the whole infidelity thing

(http://www.autoadmit.com/thread.php?thread_id=5610171&forum_id=2PHPSESSID=49d358651cc27ec1964643c2a7b5ece2#49533184)