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A principle that is used to determine if a side bitch or FWB situation is getting too serious:

-Sleeping over
-Asking to be exclusive
-Cuddling
-Kiss goodnight

If all four criteria are met at different points in the fling, you may have a relationship on your hands.
Are you sure you and her are just FWBs? Didn't you stay over at her place last night? You better watch out, that's one of the SACK Principles.

Yo dude you've met all four points of the SACK Principle! She totally wants you to ask her out.
by Sir sacksalot April 10, 2014
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Jul 24 Word of the Day
It’s an acronym standing for Can’t Remember A Fucking Thing. It’s usually used to describe embarrassment at being unable to remember someone (CRAFT moment); going onstage as the lead in the latest theatrical performance and your mind goes completely blank (CRAFT situation); the next morning after a night when you got pissed as a fart and woke up in bed cuddling a traffic cone and a string of fairy lights wound round your prick.
“Where did you go after we left the pub?”
Dunno, CRAFT.”
by AKACroatalin November 07, 2015
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