In my head, some bugs belong to categories that feel important, and yet remain hard to define and quantify: embarrassing bugs, dumb bugs, flow killers.
Somewhere in the hard-to-explain space is another tricky category: UI decisions that feel cheap.
My personal (least) favorite example of a cheap UX decision is when devs (and designers) don’t take the time to accept reasonable input into forms and force the user to input the data exactly the right way. For example, when jackson@example.com (note the extra space) isn’t accepted as an email address.