A variation on the term "pussy whipped". With the word "pistol" referring to the male genitalia instead.. Or, a talented studbroad and her toys.
"Should I invite Claryssa to the bachelorette party?"
You can, but I doubt she'll make it, That dude she's been banging has got her so pistol-whipped she doesn't even answer my texts anymore."
"WTF, why did Carlos ditch us at this suck-ass bar?"
"Oh, I think his boyfriend wanted to leave, not him, but he's totally pistol-whipped."
"Damn! That straight friend of Lisa's is cute!"
"The one in the sun-dress? She's hot and married."
"I don't care, I could pistol-whip that ass, she won't ever go home"
The female equivalent for pussy-whipped.
Your girl let you go down on her best friend last night?
Of course! She's totally pistol-whipped. I can do whatever I want and she'll be there waiting for me to come home.