For now,
Some point in all this, I pushed against her with my butt and said "Yarr!". She responded in kind and it occurred to me in a flash of brilliance.
"Say...does this make us butt pirates?"
Then I noticed that the blanket was covering her hips, so I said "Arrr, buried booty".
Somewhere in all this, the idea of what a random web image of a butt pirate would be came into her head. She figures it involves:
a) a magic marker and a mirror, or
b) a magic marker and a close friend.
Imagine being suckered with a line like:
"Say...could you help me with something?"
"Sure what?"
"I'm trying to be a butt pirate for Halloween. Here's a marker."