Abbreviation in the BDSM community, standing for "Your kink is not my kink". Complementing "YKINOK", this phrase originated on the Usenet group alt.sex.bondage, and is used to express the feeling that someone's kink does nothing for you, but without suggesting there's anything wrong with it (or, at least, nothing more wrong than there is with 'my' particular kink).
The phrase can be used to bow out of disussions on a particular topic, without causing offence to any participants.