Just noticed - setting __GL_THREADED_OPTIMIZATIONS=0 fixes this crash. I'm not sure whether it is on by default or not, if it isn't feel free to close this bug (although it'd be awesome if you'd be able to forward it to nvidia).
I have a similar setup and __GL_THREADED_OPTIMIZATIONS=1 is on for the entire system and steam does not crash. However i do get the crash with nvidia-settings (which i now launch with __GL_THREADED_OPTIMIZATIONS=0) also in libpthread.
__GL_THREADED_OPTIMIZATIONS=0)x1 2016-05__GL_THREADED_OPTIMIZATIONS=1x1 2016-05__GL_THREADED_OPTIMIZATIONS=0x1 2016-04
OS: Debian Testing (stretch) fully updated
DE: KDE5 with and without composition and LXDE
Drivers: Nvidia 361.42, but 352.79-5 from debian repo have the same issue
Crash Ids:
Reproducible by entering Big Picture and then exiting it via the menu, by playing a game from big picture and then exiting and also by pressing the stick on steam controller (to open keyboard, doesn't work) and then the steam button on it (to enter big picture mode - crash is the same).