Not sure if it's the worst code review but it's a recent one.

We don't really do code reviews where I work unfortunately but my coworker used my framework for the first time (build some nice composer libraries for cmdline projects) and asked if I could make them do autoloading.
He never used namespaces before so I was glad to help him out.

What I saw was a dreadful mess. His project was called "scripts" so good luck picking a namespace...

Than it was all lose functions in the executable file. All those functions are however called by a class in another file (if they where not calling eachother as a cascading mess). That class was extending an abstract class from my library as instructed. However I never imagined my lib being raped like that.

The functions themselves are a horrible mess. Nothing uniform completely different style (our documentation states PSR's should be used).
Parameters counts higher than 5.
Variable names like Object and Dobject (in calling function Dobject is Object but it needs a fresh one.

If statements on parameters that need basically split it in two (should simply be to functions)
If else statement with return of same variable as a single line (sane people use ternary for that)

Note that I said functions. All of it should have been OO and methods. Would have saved at least some of the parameter hell.

I could go on and on. Do I think the programmer is bad yes (does not even grasp interfaces, dep injection, foreach loops). Is this his best work no. He said that for a one of script like this it just has to work. Not going to be used elsewhere. I disagree as it is a few thousand lines of code that others have to read too.