When you're a celebrity on the red carpet, all eyes are on you. Time to crack your million dollar smile, right? Not so fast. Some stars aren't so willing to smile at photographers, and while they've been criticized by fans for having "resting mean face" these celebs have explanations for their famous frowns.

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Now, we're not saying that all famous people should smile or feel pressured to smile if they don't want to, but fans have always wondered if perhaps there are other reasons for why some celebs choose to opt out of something that the average person does every day.

For Kim Kardashian, she certainly has a reason for why she never smiles on the red carpet. The reality TV star had an epiphany after her pregnancies that changed how she felt about the paparazzi, red carpet events, and the public in general.

“Before [my pregnancies] I was always smiling, and so into being out and about,” she said in 2015. “After I had the baby, I was like, ‘These are the same people that made fun of me, and posted the stories that were so awful, calling me fat for something I couldn’t control.'”

While pregnant with North West, Kim was diagnosed with preeclampsia, which contributed to her extreme bloating that was often mocked by the public.

“I couldn’t help it, and everyone would say, ‘She can’t stop eating,’” she said. “I delivered at 180, and they were like, ‘She’s 210 pounds. She’s getting dumped because she’s too fat’ and all these ridiculous stories."

She added, “‘I don’t want to smile for them. I don’t want to be out.' Even if I was more confident, I just didn’t feel like being that girl who was going to be smiling for every photo. It changed my mood; it changed who I was; it changed my personality a lot.”

Check out our gallery to see the reasons why these celebs don't smile.