Currently working on projects for a client which is adding what should be a minor feature but it's in a horribly written codebase so there's been lots of "fix this latter" and "Add this back when working".
Or all the random comments like
#Don't change the value of this var because it breaks everything for some unknown reason
When you add a few hundred likes of code thinking you have THE solution to your issue, just to realize 90% of the way through it is totally not going to work.