Khloe Kardashian showed off her slim waist in an Instagram post, with many of her fans worrying she is becoming “too skinny.” The Good American founder, 38, posted a video of herself in front of her bedroom mirror in a blue denim bikini as she played with her hair. The bikini appears to be an item from Khloe’s new Denim Swim line, as she captioned the post “Denim Swim @goodamerican.” Along with the video, Kardashian posted a mirror selfie with her abs and stomach muscles on full display. Fans took to the comments section to express concern that the star looks too thin. “Am I the only one that …