It has become slang for making someone angry or when something or someone makes a person angry.
Today, women have picked up on this term also, using it as getting angry (but not about their hard-on going away).
He is going to piss me off (modern).
2. Get lost, go away, fuck off.
3. To get someone mad.
"Piss off cunt."
2. "You'd better piss off outta here before the cops arrive."
3. "You've gone and pissed off the IRS?Yo' in sum shit."