C++. I know it, I use it, I don't usually like it. A lot of the language just feels like a hack. I usually much prefer to write performance critical code in C but sometimes the utility of C++ or of certain C++ libraries outweighs that desire.

Also while I don't really see C++ going anywhere anytime soon, I don't really see it expanding too much either.

Both of these facts make me a lot less interested in really diving into advanced features or low level details of the language.