I was about to post something similar, CTLR+F and found this post. :)
"Deep C" illustrates the difference well between people who know C and people who know C. A bit of it is language lawyering, but some of it can be practical - although perhaps specific to certain projects or environments.
IMO this sort of knowledge is most practical if you're maintaining legacy software or in specific environments that you would otherwise be making a mistake in. People writing evergreen software or in specific targeted environments don't really need to worry about all these types of "Gotch'ya!".
