Dell computers.
I bought a brand new computer in early January. My previous computer's screen got accidentally smashed during an earthquake, and I use my computer for school, so it was very important to me to get a working computer as soon as possible. A week later, I open the package and plug the computer in, and it doesn't work. I'm not talking doesn't boot correctly, or doesn't have windows on it, I'm talking about it making a hideous beeping and grinding noise and then shutting itself off. To make a very long and irritating story shorter, six phone calls over two and a half weeks, probably 10 to 12 hours on the phone, and several outright lies about repairing my defective computer later (including the repair shop lying to Dell that they had talked to me, which believe me they hadn't), I gave up. For the final call, I told them that the options were to replace my computer or to give me a refund. They replaced it, three weeks after I got the defective computer.
I cannot imagine what they do to people who are able to turn their computers on before they stop working. I cannot imagine what they do to people who have software problems. All I know is that the simplest of problems, that of a obviously defective computer that had never turned on was such a hideous ordeal of customer service hell that I have vowed to never buy another Dell. And told my friends and family what their customer service is actually like, hoping that they won't either.