Sorry. I didn't get my PhD
in quitting.
The Big Bang Theory Season 11, Episode 15
"Why Sheldon Cooper, PhD...
The Big Bang Theory Season 3, Episode 15
If you could run out and get a PhD,
that might make her like you.
The Big Bang Theory Season 8, Episode 23
and where Leonard got his PhD,
so it may have gone downhill.
The Big Bang Theory Season 10, Episode 24
I have a PhD in astrophysics.
The Big Bang Theory Season 10, Episode 18