consistency in math btw is NEVER being able to prove both X and NOT(X) simultaneously
Correct. Which is consequently why Godel proved the eponymous Incompleteness Theorem: either a math system is too simple, i.e. incomplete (and probably not very useful overall); or it's inconsistent (i.e., it is possible to prove true "P AND NOT P").
The argument is often told as a statement in prepositional calculus. The statement is constructed as an interpreter of prepositional calculus, operating on some given number. It just so happens, the number is constructed to code for an inconsistent statement. (A statement in PC can only be built stepwise from the rules of the system; but any finite number can be constructed with finite steps, arbitrarily without the code equivalent being subject to rules.*) It's the logical equivalent of (and predecessor to) the Halting Problem.
*In modern terms, a sort-of equivalent is coding in any syntactically checked high-level language, versus loading a (relatively large) number that itself just so happens to be machine code. The code compiled from the language must follow the structure of that language (of course, practical computing languages are not made nearly so limited as mathematical systems are, so it is still possible to express the Halting Problem in, say, a few dozen statements...), whereas the number is completely arbitrary and unstructured (until something happens to read that number as some coded system, and it turns out to have interesting effects).
Tim