Oh man. Mine are the REASON why people dislike PHP.

Biggest Concern: Intranet application for 3 staff members that allows them to set the admin data for an application that our userbase utilizes. Everything was fucking horrible, 300+ php files of spaghetti that did not escape user input, did not handle proper redirects, bad algo big O shit and then some. My pain point? I was testing some functionality when upon clicking 3 random check boxes you would get an error message that reads something like this "hi <SENSITIVE USERNAME DATA> you are attempting to use <SERVER IP ADDRESS> using <PASSWORD> but something went wrong! Call <OLD DEVELOPER's PHONE NUMBER> to provide him this <ERROR CODE>"

I panicked, closed that shit and rewrote it in an afternoon, that fucking retard had a tendency to use over 400 files of php for the simplest of fucking things.

Another one, that still baffles me and the other dev (an employee that has been there since the dawn of time) we have this massive application that we just can't rewrite due to time constraints. there is one file with (shit you not) a php include function that when you reach the file it is including it is just......a php closing tag. Removing it breaks down the application. This one is over 6000 files (I know) and we cannot understand what in the love of Lerdorf and baby Torvalds is happening.

From a previous job we had this massive in-house Javascript "framework" for ajax shit that for whatever reason unknown to me had a bunch of function and object names prefixed with "hotDog<rest of the function name>", this was used by two applications. One still in classic ASP and the other in php version 4.something

Legacy apps written in Apache Velocity, which in itself is not that bad, but I, even as a PHP developer, do not EVER mix views with logic. I like my shit separated AF thank you very much.

A large mobile application that interfaced with fucking everything via webviews. Shit was absolutley fucking disgusting, and I felt we were cheating our users.

A rails app with 1000 controller methods.

An express app with 1000 router methods with callbacks instead of async await even though async await was already a thing.

ultraFuckingLarge Delphi project with really no consideration for best practices. I, to this day enjoy Object Pascal, but the way in which people do delphi can scare me.

ASP.NET Application in wich there seemed to be a large portion of bolted in self made ioc framework from the lead dev, absolute shitfest, homie refused to use an actual ioc framework for it, they did pay the price after I left.

My own projects when I have to maintain them.

The temple at Delphi stated "Know Thyself".
But it's a much bigger issue in JavaScript.