I don’t mind bad code, I know why it happens and a lot of good points are made here in the comments.

What I cannot stand and can barely tolerate is kruft and sloppiness. massive sections of commented out functions, leaving the poor guy to come along 2 years later wondering if it was important or why it was left there. Unused functions. bad, inconsistent, or nonexistent naming conventions. Terrible or annoying file/project structure.

None of this stuff has to be. Not doing this stuff requires a bare minimum of effort and time and doesn’t require any familiarity with a codebase. It’s a lack of professional pride, and that deeply annoys me when I inevitably have to clean it up because it’s an unreadable mess.