I believe the back-scratching METAPHOR
describes a quid pro quo situation...
The Big Bang Theory Season 2, Episode 16
Yeah, me, too. I was stuck for a METAPHOR.
The Big Bang Theory Season 9, Episode 12
They say it's the perfect METAPHOR
for my incandescent talent.
The Big Bang Theory Season 2, Episode 4
That was a beautifully written
penis METAPHOR.
The Big Bang Theory Season 5, Episode 1
Wow, was that your first ever
sports METAPHOR?
The Big Bang Theory Season 12, Episode 10