Not really most painful, but definitely most painful of the recent bunch..
// yup, a bunch.. I've managed to fuck up a little on every thing I did that day :/ little friday the 13th for me, especially as I went on sick leave the next day and had to fixup my fuckups with a friggin migrane..

Anyways, I was fixing fallback to some default value in plsql.. before it didn't check what the input format was and simply relied on certain format, parsed that and converted to number..threw an error, duh!

I fixed it somehow elegantly to check with regex if the format is as expected and if not default to xy value..and if format is as expected to parse out the number..except that when I copied (or typed?! for the sake of me, I cannot recall how the fuck I managed to fuck this up) over the code to the package I didn't see additional [ at the begining, so everything went to the default.. Most embarrassing part is I commented everything, how it should work, use cases, what the input was and what was expected output..and failed to see the friggin extra [..
It was fixed easily, the extra [ stood out later when I saw the code, but it bothers me how I managed to overlook that in the first place. I think I need a vacation.. but have to fix other fuckups first.. :/