Senior enough, and skilled enough in particular low level arts, that I can set my own terms.

And I do "weird low level crap." Generally if I'm interacting with the kernel, it's from below. Think introspection, emulation, hypervisors, "state analysis of a running kernel," firmware weeds, security analysis, etc.

If you know a bitter mid-to-late-40s sort who's been in the deep weeds and the security weeds long enough to carry a powered off flip phone and genuinely hate what we've done with computers, imagine that, and you're pretty close.