
A, that was not a joke,
that was a SINCERE request.
The Big Bang Theory Season 6, Episode 24

And I want you to know that
that is SINCERE. I do feel bad.
The Big Bang Theory Season 9, Episode 13

I sense that's not SINCERE,
although I have no idea why.
The Big Bang Theory Season 3, Episode 11

...and if I can figure out a way to do so
and sound SINCERE, I will.
The Big Bang Theory Season 4, Episode 9

Not to "Sin City" but to "SINCERE city."
The Big Bang Theory Season 9, Episode 13