
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

That was a beautifully written
penis METAPHOR.
The Big Bang Theory Season 5, Episode 1

I believe the appropriate METAPHOR here
involves a river of excrement...
The Big Bang Theory Season 2, Episode 8

I believe this is an extension
of the death METAPHOR.
The Big Bang Theory Season 2, Episode 8