If you were 16, and your parents caught you texting “Netflix and chill?” to your girlfriend, they might think you were proposing an innocent night of watching Chopped on the couch.
-Kevin Roose, fusion.net
It is a typical parental strategy to check a child's texts to make sure they aren't participating in disapproving activities. Having sex can be one of these disapproving activities in some households. Roose makes an accurate observation of many high school aged males. To someone who doesn't already know how "Netflix and chill" is meant to be interpreted, it seems like a harmless session of hanging out with a friend. This is why many parents wouldn't think twice if they saw those words in their child's texts.