
I'm getting my PhD.
The Big Bang Theory Season 4, Episode 24

"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

Sorry. I didn't get my PhD
in quitting.
The Big Bang Theory Season 11, Episode 15