Baby, I won't treat you like he did
But I thought negation caused dopełniacz / genitive...
Yes, but only if the positive sentence took Accusative (which happens very often, but not all the time).
Here both the positive and negated sentence take Instrumental.
Why is it not declined for instrumental?
If you refer to the hint, under "tamtym", - it is both locative and instrumental, and unfortunately hint shows only locative.
but "tamtym mężczyzną" is instrumental
My grammar book gives instrumental singular endings as -em or -iem. Where does the a squiggle fit in?
"mężczyzna" is (logically) masculine, but it's one of those few masculine words that end with -a, and therefore it undergoes declension as if it was feminine.
Why is it the instrumental case here? Is "jestem mezczyzna" also instrumental case and was i just not aware? Or does it take instrumental because of "tamtych"?
"jestem" has been instrumental all throughout the course.
Instrumental when used with nouns. If it's followed by an adjective only, then it's in the nominative case, e.g. "jestem silny", not "jestem silnym".