Broken down, "pissed-up" means inebriated or
drunk. A "slapper" is, well, a slut. Or, a
woman of
loose morals. So, a "pissed up slapper" is also known as a drunken trollop or whore.
"Lets go to the bar tonight and pick up a
couple of pissed up slappers." "Check that pissed up slapper going down on
Mark in the
corner." "It's a sure thing cause she's a pissed up slapper."