My prefix is man.
My suffix is sharp.
My infix is man.
The whole is hard.
What am I?
You could be
adamantine
My prefix is man.
Adam - first man
My suffix is sharp.
Tine - a sharp, projecting point or prong, as of a fork.
My infix is man.
Man - man
The whole is hard.
adamantine - too hard to cut, break, or pierce.