A Mexican common saying meaning that If you drink on Monday you drink all week. In spanish in rhymes: Ley gitana- Si tomas en lunes... tomas toda la semana.
If you drink alcohol on Monday the gypsy law requires you to drink alcohol all week, otherwise a curse will fall upon you and no one wants a gypsy curse.
- Oh man, I'm so drunk right now
- Dude, it's Tuesday what the fuck?
- Yeah bro but I drank yesterday and you know what the gypsy law says... if you drink on monday you drink all week. Hold my beer bro *pukes on himself*
- Hey dude! Let's go grab a beer
- Dude, no, be careful. Today is Monday.
-So what bro?! Let's get shitfaced
- No dude, I don't mess around with the gypsy law. If you drink on Monday you have to drink all week or a gypsy curse will fuck you up and I don't want my kids to be born with bad luck.