Diacetyl hasn’t been used in any reputable vape juice brand in like a decade(and is banned in EU), and there’s also absolutely no evidence that the juices that did contained enough to cause popcorn lung. There’s a reason it’s called popcorn lung, because the most likely person to get it is one who works in a popcorn factory and is exposed to industrial quantities of Diacetyl, day after day for likely 10-12 hour shifts. The difference in dosage is astronomical. If you’ve ever worked in a kitchen, you’ll know how grease vapors in the air will absolutely coat you in a film of yuck. Imagine that same idea but instead of grease it’s Diacetyl coating everyone and everything in the factory.