
I believe the back-scratching metaphor
describes a quid PRO quo situation...
The Big Bang Theory Season 2, Episode 16

There's PRO football, college football,
high school football, peewee football...
The Big Bang Theory Season 3, Episode 6

Pro tip: if you find
strong women sexy,
The Big Bang Theory Season 12, Episode 19

- Where do you stand on it?
- Strongly PRO.
The Big Bang Theory Season 6, Episode 1

lt behooves you to be a PRO,
that's all. That's the fiction.
So chop-chop.
Breaking Bad Season 4, Episode 4