1. Anything goes on October 31st. Well, ish. Within reason

'Halloween is the one night a year when a girl can dress like a total slut and no other girls can say anything about it'

The mantra of your teens and early 20s. The only thing holding you back now is weight gain, dignity and a husband. And even they don’t hold you back some years.

2. Knowledge is nature’s volumiser

'That's why her hair is so big – it's full of secrets.'

Who needs Elnett or a Babyliss Big Hair? 

3. Always layer (or remove jumpers in private, just in case)

'My T-shirt is stuck to my sweater, isn’t it?'

See also: try to avoid talking to your boss when your shirt is see-through.

4. When the going gets tough, the tough go shopping

'Get in, loser. We’re going shopping.'

In these days of online shopping, don’t forget the old-fashioned pleasures of an “offline” mall trawl. I know, right?

5. Don’t force a trend

'Gretchen, stop trying to make ‘fetch’ happen!'

You’re a trailblazer, sure, but trends need to grow organically. Even if you come up with exotic reasons like, “Oh, it's like slang, from... England."

6. If you can't say something nice, don't say nothin’ at all (aka The Tao of Thumper)

'Calling somebody else fat won't make you any skinnier. Calling someone stupid doesn't make you any smarter.'

If only cyber-bullies, the Daily Mail, Twitter trolls, haterz and Katie Hopkins were as wise as Tina Fey’s script, the world would be, like, totally a way better place.

7. Nobody owns a look

'You'd know that I'm not allowed to wear hoop earrings, right? Two years ago she told me hoops earrings were *her* thing and I wasn't allowed to wear them anymore. And then for Hanukkah, my parents got me this pair of really expensive white gold hoops and I had to pretend like I didn't even like them. It was so sad.'

That IS sad. The lesson here: we all share ownership of fashion. It’s like a lottery syndicate, civic car park or municipal swimming baths. 

8. Don’t be a dumbass

'You don't have to dumb yourself down in order for a guy to like you.'

Unless the guy’s deeply dumb, in which case, he’s not worth it anyway. Feel me?

9. Vintage is your birthright

Regina: Oh my God, I love your skirt! Where did you get it?

Lea: It was my mom's in the '80s.

Regina: Vintage! So adorable.

Lea: Thanks.

Regina: [after Lea walks away] That is the ugliest effing skirt I've ever seen.

OK, ignore the last bit. Vintage IS so adorable, especially when it’s passed down by your mum. Well, you deserve some payback for those long phonecalls where she tells you about tedious things in enormous detail. 

10. Trust your gut instincts

'Whatever. I'm getting cheese fries.'

Confucius, he say sometimes the wrong thing is the right thing. Well, it was either Confucius or Regina George. Much the same thing.

11. Find your signature scent

Janis: What IS that smell?

Cady: Oh, Regina gave me some perfume.

Janis: You smell like a baby prostitute.

Probably not the sophisticated after-dark aroma you were aiming for.

12. Style out any wardrobe malfunctions

Carry it off confidently enough and it’ll look deliberate. Or at least not totes cringe. See also: 'I saw Cady Heron wearing army pants and flip flops, so I bought army pants and flip flops.' How very All Saints-popping-out-for-milk.

13. Don’t cramp your own style

'Ugh, lipgloss.'

Regina won’t let Aaron kiss her in congratulation after Santa’s Helpers’ triumphant rendition of Jingle Bell Rock at the winter Talent Show. Hello? Take the snog, then reapply with a Juicy Tube. So fetch.

14. Size is non-negotiable

Regina: Ma'am, do you have this in the next size up?

Saleslady: Sorry, we only carry sizes 1, 3 and 5. You could try Sears.

Never squeeze into a smaller size, hoping you’ll 'slim into it'. That way, madness and wasted money lie. If the snooty boutique can’t help ('Big mistake. HUGE'- sorry, different film), a bigger branch or mail order often can.

15. Enough already with the slut-shaming and name-calling

'You all have got to stop calling each other sluts and whores. It just makes it OK for guys to call you sluts and whores.'

The sisterhood has it hard enough without us hating on each other, so let’s put a stop to what Tina Fey calls 'girl-on-girl crime'. Yeah? Yeah! High-five! Come on, gimme some skin. Don’t leave me hanging.

16. Don’t wear anything that requires explanation

'I’m a mouse. Duh!'

When your outfit needs accompanying notes, you’re probably trying too hard. Or can you predict the weather with your boobs too?

17. Retain a sense of proportion

'I mean, it’s just plastic.'

When you’re blinded by stress, things seem like a bigger deal than they are. Step back, take a breathe and then, and only then, panic. Complete with flappy hands and neck rash.

18. Innovate, don’t imitate

'On Wednesdays, we wear pink.'

Synchronised watches, good. Synchronised dressing, bad. Synchronised swimming, weird but good.

19. No-one notices your body hang-ups except you

Karen: God. My hips are huge!

Gretchen: Oh please. I hate my calves.

Regina: At least you guys can wear halters. I've got man shoulders.

Gretchen: My hairline is so weird.

Regina: My pores are huge.

Karen: My nail beds suck.

Cady: I have really bad breath in the morning.

Everyone has weird little things they think are wrong with their body. Just don’t go on about them or get them out of proportion. Except you with the man-shoulders and sucky nail beds, you really are gross. Just kidding.

20. If dresses aren’t your thing, work a suit

Janis rocks a mannish tux at Spring Fling. Totally like Angelina at the BAFTAs.

21. Rip up the rulebook

'You can’t wear a tank top two days in a row and you can only wear your hair in a ponytail once a week. Oh and we only wear jeans or trackpants on Fridays. If you break any of these rules, you can’t sit with us at lunch.'

Shut UP. I’m getting cheese fries.

22. We’re all the same underneath

'She’s not even that good-looking, if you really look at her. I have this theory that if you cut off all her hair, she'd look like a British man.'

Wouldn’t we all, sweetie? Love ya!

23. Geek chic never goes out of style

Joining the Mathletes wasn’t social suicide and Li-Lo also got an on-trend leather-sleeved jacket out of the deal. Listen to math enthusiast/badass MC Kevin Gnapoor: “Don’t let the haterz stop you from doing yo thang.”

24. The ex factor

'Irregardless, ex-boyfriends are just off limits to friends. I mean that's just like the rules of feminism'.

This is inarguable feminist truth, probably written by Germaine Greer, Andrea Dworkin, Simone De Beauvoir or someone. However, there’s no such word as “irregardless”.

25. Friends get the right of veto

'Well, I mean, you wouldn't buy a skirt without asking your friends first if it looks good on you. It’s the same with guys.'

Other things men have in common with skirts: um… different lengths depending on the weather? Let’s not go there.