Can you guess what's in there?
If there's one way of finding out which trends were massive in 2015, it's got to be looking at YouTube's most viral videos.
And rather than trawling through the billions of videos on the social media site ourselves, they've helpfully compiled a catchy video - which will probably go viral in itself - showing us the best moments of the year.
With background music composed by The Hood Internet and Avicii, the video features the year's most memorable songs, including Omi's Cheerleader, Justin Bieber's What Do You Mean and Major Lazer and DJ Snake Ft. MO's Lean On.
It also features Silento's hugely memorable video Watch Me (Whip/Nae Nae), with YouTube's very own adaptation of the famous school gym video, with a whole host of dancers dressed in outfits through the ages. The amazing pint-sized dancer from the original video even makes an appearance.
Shia LaBeouf's unforgettable video in which he commanded us all to 'just do it' was also parodied in a variety of languages. That's one viral vid we'll never be able to forget, unfortunately.
You might spot some of your favourite stars in there too - like James Corden, Zoella and Karlie Kloss, all doing their bit to remind us how quickly the year has gone.
The video also took a look back at some of the most viral trends of the last ten years, including the memorable line 'Charlie bit my finger', the Ice Bucket challenge and Rebecca Black's infamous song Friday.
You can watch the video below...
Perhaps the most painful thing of all is knowing that in another ten years, when we watch this back, songs like Cheerleader and What Do U Mean will seem quaint and retro, and kids born in 2015 will be laughing at us for ever dancing to Watch Me (Whip/Nae Nae).
Do you think any important trends were left out? Let us know @marieclaireuk
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