The Plastics are a group of popular girls in the movie "Mean Girls" who have a set of rules that they follow. The rules are designed to keep the Plastics in control and to maintain their popularity. Here are some of the rules mentioned in the search results:

• "On Wednesdays, we wear pink"
• "Don’t wear a tank top two days in a row"
• "You can only wear your hair in a ponytail once a week"
• "You can only wear jeans or track pants on Fridays"
• "You can’t buy a skirt without asking your friends first if it looks good on you"
• "Ex-boyfriends are just off-limits to friends"
• "Tank tops are in"
• "Hoop earrings are Regina’s thing"

Its worth noting that some of these rules are superficial and arbitrary, and they are not necessarily meant to be taken seriously.