Something I never understood: Superman-like characters who are so tough they can get hit with lava, acid, tank round, etc and not even FEEL it. How on each can they feel that at normal human speed friciton?

The same way that they can hear conversations miles away without being deafened by ordinary conversation or shoot lasers out of their eyes without burning off their corneas or any of the millions of blatant physiological contradictions inherent in such characters.