Discussion on answer by Wesley Long: How can I convince my manager that I work better with a vertical monitor?

When asking IT, in order to not appear to be undermining your boss's [infuriating] need for control, I would copy the boss in and present it as innocently as possible, presenting them as the bad guy, just like your boss pretended. Ham it up: "Hey, I just found out that there is an IT regulation against having my monitor sideways. I think it's really important to my productivity. Windows natively supports screen rotation, (show screenshot example) and the monitor pivots...." yada yada, end with the gist but not verbatim, "I'm not sure why you're making such an unreasonable deal out of this."

part 2: In my estimation, they will likely hit back hard about how asinine that is to suggest that you can't do it that way. In which case, you win this one. Now, they might be aware of your boss' issues with control -- surely they are by now -- and might be more diplomatic with their reply, but either way, I think you win with this method. Except you're still losing by being there. I know you didn't ask but assuming that IT doesn't come back saying "no" as well, you should get a new job ASAP. However, I'm concerned (for your sake) that you appeared willing to live with this behavior