The "Grad school: It seemed better than getting a real job" t-shirt from PhD Comics.
And the fantastic Think Geek t-shirt from here. The concept of a non-medical doctor is still a new one for many people I have encountered since being offered a Doctor of Philosophy position.
For an etymology lesson I defer to Mark at allexperts.com who explains:
The earliest use of "doctor" in WRITTEN English was in 1303, but the term applied to "doctors of the Church," meaning "learned men in the scriptures."
It was not until 1377 that it was used in the sense of "medical doctor," or one who treats illnesses or diseases.
[a. OF. doctor (-ur, -our, -eur), ad. L. doctor, -rem teacher, agent-n. from docre to teach.]
The entry from the Oxford English Dictionary above traces the word's origin -- from the Old French "doctor" from the Latin "doctor," meaning "teacher." And that noun came from the verb "docre" which meant "to teach."
Oh, so what you are saying Mark is that doctor's were learned folks like teachers and the term was taken up for medical doctors because they are learned folks also - not because it means to operate or prescribe antibiotics. Hmmmm... now I just need to get one (a doctorate I mean, not a doctor)!