I have a PhD in astrophysics.
The Big Bang Theory Season 10, Episode 18
"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 23
I have a PhD from Cornell University.
The Big Bang Theory Season 6, Episode 22