1. You know they'll never spill your deepest, darkest secrets in life. (Especially THAT one.)
2. You have 'a song'. Heaven help anyone in a 3-metre radius of either of you when it comes on during a night out and you dance your little hearts out.
3. They'll always tell you when they have any of the following: an eye bogey, food in your teeth, smudged eyeliner, gunky lipstick, a gappy fringe.
4. You have your own emoji language. Only you two will ever understand the deep, deep significance of 👻🎈🎺.
5. They don't just know your Nando's order. They know which sauces and bottomless drink you'll want, too.
6. If you two take a selfie and they look great but you look a bit crap, they'll retake it until you both look equally awesome. Sacrificing a really decent selfie is a mark of true friendship.
7. You can help yourself to their stuff without feeling dead rude. Kirby grips, tampons, Oreos. Friendship knows no bounds.
8. Your in-jokes never get old. If anything, they get even funnier with time. (Except to everyone in the world that isn't you two.)
9. You can still have fun together when you're both at your lowest, such as during monumental hangovers or really hellish traffic.
10. You can have fun when doing absolutely nothing, too. You don't need activities when you have each other.
11. They know your pernickety Starbucks order by heart. (And your 3am kebab shop order.)
12. Their parents treat you like one of the family. You've definitely witnessed them snog, scream at each other and everything in between.
13. They never leave you hanging when it comes to likes on Facebook and Instagram. That's basically the first rule of being best friends for life.
14. You're absolutely horrible to each other, but you both know it's just jokes.
15. Your silences aren't awkward at all. Everyone needs some down time, and you get that.
16. Even if weeks go by without hanging out because life gets in the way, when you finally do see each other, it's like it was only yesterday.
17. You know each other's screen lock code. That's trust right there.
18. They always fight your corner. God help anyone that slags you off, because they will feel the BFF wrath.
19. They always help you make the right decisions, even when drunk. Such as NOT drunk dialling you-know-who.
20. You NEVER have to settle for a less-than-perfect photo of yourself on social media. Best friends means taking 45 photos of each other before it's just right, no questions asked.
21. They'll be straight with you if you're about to make a really bad decision. Be it about lunch or life.
22. You know almost as much about their bodily functions as you do about your own.
23. They know exactly how you like your tea. And coffee. And toast.
24. No matter how unpredictable life is, you KNOW they will always have your back, and vice versa.
Best Friends. Forever.