I've got some doozies...
... mostly involving Citrix. We had out VAR come in to do a very specific setup involving a load balancer (Citrix Netscaler) and a security appliance made by a large company with a bridge as part of their logo. Neither of us knew the exact process to get the netscaler to do what we wanted it to do, so we called the help desk for Citrix. They kept insisting that it could do it, suggested a configuration, we tried it, it didn't work worth a hill of beans, they kept insisting, we asked to escalate, the second level techs parroted the same thing back to us, and finally we got up to one of the engineers who told us five minutes after reading through three hours worth of logs, escalations, and tries that "no, it can't do what you want it to do, it's not designed to do that."
our VAR was incandescent by the time that happened; after he got off the phone, he had some exceptionally creative entries that I added to my Book Of The Profane and Obscene. Shortly thereafter, we dumped the netscaler for an F5, which took all of 15 minutes to set up and deploy the configuration they were looking for.
Their support group also had no idea how to extend the log file drive on the appliance, because when it filled up, the UI stopped responding and the only way to fix it was to go on the machine's console and manually clear out space, and there was no facility to auto-purge old log files.
I've done the whole entire "ok, give me a minute to do that" [waits exactly 60 seconds] "nope, machine is still emitting ectoplasm and asking for the Keymaster of Gozer. NOW will you send a tech with a new mainboard??" thing with hardware support.
HPE Nimble gets a mention for "when we said we are dropping support for [product line] we mean it- no firmware updates, no documentation, and no replacement hardware from our VARs- you'll have to get replacement hardware on the grey market as refurbished units, NOS from some backwater warehouse in North Dakota that got a case of the things by mistake and manages to sell one when they find the case in the back."
For kudos, since I am naming and shaming up there, NEXSAN's support has been... magical. I called them one day in a right panic because the thing was showing multiple failed drives (due to a firmware bug) and the tech that connected with me set up a screen sharing session, pointed me at a specific web page on the machine, and un-failed the drives, bringing it all back to life. He then gave me a link to update the firmware on the device. Other times I've contacted them for hardware issues, and they were both spot on, had the replacement hardware to me within 72 hours, and also made sure we were good with firmware. (and after we let the support lapse on them, they did inform me that "no you have to buy our disks, because we do things with signed firmware that can't be duplicated; even though you are out of support, we'll cheerfully sell you replacement drives."
Cisco... gets a "meh" from me. If I have bad hardware that's provable in the SEL logs (i.e. bad memory sticks) or a failed drive on their UCS systems, as long as I upload the support bundle when I open the case, I usually (~90% of the time) get a response of "yep, it's broken, where do you want the replacement part sent". The other 10% of the time, I have to play the "reseat failed component" game.