Mobile - I don't use iOS, and Android is a nightmare platform from hell to develop for
Anything to do with 3D graphics - They're tedious and give me a headache
Any more about Windows or Mac OS than I absolutely have to - Nothing personal against them, I use them both plenty as an end user, but learning to do something that only works on one OS and that OS isn't Linux sounds like a big waste of my time.
ahhaha I don't know if it's true but I feel it's the most hyped tech in the history of hype