A, that was not a joke,
that was a SINCERE request.
The Big Bang Theory Season 6, Episode 24
If you're interested in making
a SINCERE effort to be a good teacher...
The Big Bang Theory Season 8, Episode 2
Okay. Now, see you look SINCERE
but your words are completely false.
The Big Bang Theory Season 10, Episode 6
...and if I can figure out a way to do so
and sound SINCERE, I will.
The Big Bang Theory Season 4, Episode 9
I sense that's not SINCERE,
although I have no idea why.
The Big Bang Theory Season 3, Episode 11