My peeve is products made "easy" to use, in a way that makes explaining them extremely difficult. Two top examples are:

URL bar in browsers which doubles as a search bar. Good luck explaining why if you type in an exact existing address, you will get there, but otherwise (typo, extra space), you will end up on Google.

Apple's iMessage. Your message will be sent to your contact using one of three protocols: SMS/MMS, iMessage or RCS. This is almost entirely opaque, and I even had to explain to a tech-savvy person why videos they send me look like blobs.