Celebrities are just as susceptible to social media peer pressure as the rest of us, it seems. On Tuesday, the 35-year-old actress Sienna Miller announced that she finally "gave in" and made a personal Instagram account with an aptly apathetic handle, @SiennaThing.

"Hello World Wide Web," she captioned her cheeky first post, in which she wears a public relations-friendly "We should all be feminists" t-shirt by Dior. Scrawled in marker across the palms of her hands is simply the word "Greetings."

Since joining, Miller has also posted a promotional poster for her new role in Tennessee Williams's Cat on a Hot Tin Roof, which opens at the Apollo Theatre in London on July 13. This is maybe evidence that her decision to join Instagram was more promo pressure and less peer pressure—although perhaps those are the same thing when you're a celebrity.

In the case of Miller, social media pressure is anything but average, seeing that her "peers" include famous actors and models with millions of followers. You either go all the way, and treat your Instagram account as an extension of your professional self, or you do what Miller has done until now, which is abstain. There's no in-between when it comes to celebrities on social media.

Thankfully for Sienna Miller though, she's got friends (and now followers) in high places. Cara Delevingne, for example, welcomed her to the platform by sharing the news with her own 40 million followers. "My snoyster oyster is on instagram!" Delevingne wrote to accompany a cute photo of her and Miller.

As a result, Miller has since gained almost 80,000 followers. Greetings, indeed!

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