I know it can be awkward to tell someone she has food in her teeth, or that her skirt is tucked into her underwear, or whatever, but someone has to tell Kylie Jenner there are holes in the back of her jeans. She'd want to know.
Like, the person who took this photo and uploaded it to Kylie's Instagram could've said, "Hey, this is a good photo and I'm going to post it but two large slivers of your butt are visible in it, FYI."
There is a chance these holes are deliberate and Kylie is using them as ventilation — a tactic she's used before when wearing cold-weather clothing in the summer heat. Alas, there's no way of knowing.