Microsoft's "documentation". It's just abysmal.

any one of those facebook/instagram/reddit etc which pretends not to work on a regular browser so they can sell you their app, broken buttons, fucked layout, mostly bot content... it's hard to pick they're all shit

Anything SharePoint.
So many companies end up using SharePoint for "knowledge management" not realizing they are dooming their knowledge to be lost in some byzantine hole of information where no one will ever be able to find or use it ever again. Worse, as more knowledge is yeeted into the pile, the search becomes better and better at presenting outdated, or irrelevant information. So, you will have new employees who find a process which is 5-10 years out of date, completely wrong, but it looks official and the links still work for some gods forsake reason. Of course, the right information is in SharePoint somewhere, but it's probably locked behind a site with broken permissions, in a document library in a Word document which isn't properly indexed and there's 4 different versions of the same document with names like "New procedure_v3_DRAFT_bob's edits.docx", because no one understands how file versioning works.

Microsoft 365 admin portal. There's always something that's broken on it or takes a very long time to load for no good reason.

Every time I am forced to open the IBM documentation, I not only not find what I was looking for, I am extremely frustrated because I literally couldn't tell that the information is not there. The site is slow, the search is fucked, and I hate how corporate it is.

Same goes to Microsoft documentation.

My old geocities website where I list my top 5 Linkin Park songs, has badgerbadgerbadger in a grid background and plays pretty fly for a white guy at full volume.

Debian's site is awful. I hate when there's some giant, useless picture that you have to scroll an entire screen-length past, and then everything is still absurdly spaced apart. Look at those dumb, giant icons. Compare to debian's site from 2018: https://web.archive.org/web/20180208023935/https://www.debian.org/ which is so much better. And actually contains information relevant to why you would go there in the first place.

http://horserentals.com/

Facebook. Dark patterns and malicious coding GALORE. Its torture.

I don't really know if it qualifies as worst, but Costco's website is the slowest website I have used in recent history.

It's so painful to use. It takes three to ten seconds for each click to take effect.

Drives me batty.

But also, ebay has gone in the shitter. Amazon is just the fucking worst. Google itself is terrible because its results lie to you and it will never show you the website you're looking for, no matter what, because as long as you don't find the website you're looking for, you're staying on Google.

Patreon is up there.

Most of the page is just wasted white space, the menu collapses randomly to little icons (guess so we can have more whitespace), the video feed is a small strip between the white space with only one video per column, ensuring you can never fit more than 3 on the page. The player somehow stretches across the fill page width, replacing some of the wasted white space with wasted black space. And that's just the interface.

You also have to unsubscribe from like 7 mailing lists per creator, individually, no option to disable entire lists (or they don't work). They also randomly add new lists which are by default enabled so you have to go through all your creators again. Oh, and if you click too fast when disabling their settings, sometimes it won't save ... at some point I just made an outlook rule auto-flagging all their mails as spam, because fuck that.

youtube, google classroom.. google's stuff are all shitty nowadays. awfully slow and buggy for no reason

Any Japanese website. They insist on having every single inch of the screen filled with something, they have a ton of things moving across the screen, flashing, scrolling, dancing. Its crazy and the worst part is I can't read a thing on it.

Not retaining account information sounds like a feature to me.