Hooks that have too soft of steel, and straighten out during use, including in the vise or on a fish (and someone once told me that was impossible here, even though it has happened to me many many times. Reality trumps theory). Cabelas brand dry fly hooks come to mind. Stopped buying those many years ago. A subcategory of this is hooks whose points turn over if they touch a rock or any other object. Small mustad hooks come to mind. They didn't used to do that. Couple packages of these, I quit buying Mustad.

Poor inspection/flawed manufacture. Hooks that have parts missing, are incompletely made, open eyes, no bend, line stamped across them almost cutting them in half...etc. Dai Riki 135s. After several packages of these many years ago, with about a 6% (3 per box of 50) nonfunctional hook rate, I quit buying them. Now in thousands of Dai Riki 700s, I have only found two bad hooks. Go figure.

I fully expect some of you to loudly proclaim that you have never had this happen with these hooks. You can have my share of the market for those, then. I will spend a couple more cents per fishing trip and stick with the hooks that don't let me down.