We're using a ticket system at work that a local company wrote specifically for IT-support companies. It's missing so many (to us) essential features that they flat out ignored the feature requests for. I started dissecting their front-end code to find ways to get the site to do what we want and find a lot of ugly code.
Stuff like if(!confirm("blablabla") == false) and whole JavaScript libraries just to perform one task in one page that are loaded on every page you visit, complaining in the js console that they are loaded in the wrong order. It also uses a websocket on a completely arbitrary port making it impossible to work with it if you are on a restricted wifi. They flat out lie about their customers not wanting an offline app even though their communications platform on which they got asked this question once again got swarmed with big customers disagreeing as the mobile perofrmance and design of the mobile webpage is just atrocious.

So i dig farther and farthee adding all the features we want into a userscript with a beat little 'custom namespace' i make pretty good progress until i find a site that does asynchronous loading of its subpages all of a sudden. They never do that anywhere else. Injecting code into the overcomolicated jQuery mess that they call code is impossible to me, so i track changes via a mutationObserver (awesome stuff for userscripts, never heard of it before) and get that running too.

The userscript got such a volume of functions in such a short time that my boss even used it to demonstrate to them what we want and asked them why they couldn't do it in a reasonable timeframe.

All in all I'm pretty proud if the script, but i hate that software companies that write such a mess of code in different coding styles all over the place even get a foot into the door.

And that's just the code part: They very veeeery often just break stuff in updates that then require multiple hotfixes throughout the day after we complain about it. These errors even go so far to break functionality completely or just throw 500s in our face. It really gives you the impression that they are not testing that thing at all.

And the worst: They actively encourage their trainees to write as much code as possible to get paid more than their contract says, so of course they just break stuff all the time to write as much as possible.
Where did i get that information you ask? They state it on ther fucking career page!

We also have reverse proxy in front of that page that manages the HTTPS encryption and Let's Encrypt renewal. Guess what: They internally check if the certificate on the machine is valid and the system refuses to work if it isn't. How do you upload a certificate to the system you asked? You don't! You have to mail it to them for them to SSH into the system and install it manually. When will that be possible you ask? SOON™.
At least after a while i got them to just disable the 'feature'.

While we are at 'features' (sorry for the bad structure): They have this genius 'smart redirect' feature that is supposed to throw you right back where you were once you're done editing something. Brilliant idea, how do they do it? Using a callback libk like everyone else? Noooo. A serverside database entry that only gets correctly updated half of the time. So while multitasking in multiple tabs because the performance of that thing almost forces you to makes it a whole lot worse you are not protected from it if you don't. Example: you did work on ticket A and save that. You get redirected to ticket B you worked on this morning even though its fucking 5 o' clock in the evening. So of course you get confused over wherever you selected the right ticket to begin with. So you have to check that almost everytime.

Alright, rant over.
Let's see if i beed to make another one after their big 'all feature requests on hold, UI redesign, everything will be fixed and much better'-update.