In several 12-step fellowships, it is generally looked down upon and discouraged (not by everyone) to sleep with someone under a year clean, especially if you have over a year clean. The loophole refers to catching the "newcomer" before he/she even gets clean, therefore providing a valid excuse for the incident(s) to be perfectly moral and justified.
Yo man, I'm thinking about trying to fuck Sheila, she's only got like 37 days though..." --"Definitely do it, who gives a shit what people say, that's 37 days too many in my opinion. I just fucked a girl who had zero days a few nights ago, real talk." "Word, that's awesome - you found the loophole.