Manpain is a dismissive term for stock male character behavior that satisfies conditions optimal for eye-rolling.
The difference between manpain and a man in pain is that manpain entitles the man to be as destructive as he wants until his manpain is gone, without consequences.
It’s a cliche that has to die for many reasons, but for our purposes it’s because no one can take it seriously anymore. It’s so overused it has achieved escape velocity right into self-satire.
Manpain scripts, of course, viciously assault/destroy female characters as a license for manrevenge, but that’s just the tip of the boring, outdated, unacceptable iceberg.
Eradicate manpain from your protagonist. Not just because it’s lazy and repellant, but because it’s the mortal enemy of drama.