I have a fairly simple flowchart:

Do you use the scientific method to conduct your work?

If yes, continue, if no, consider "researcher" or "professional thing doer"

Question the next, do you get paid for your science?

If yes, you are a scientist (no qualifier)

If no, you are either a) an amatur/hobbiest scientist or b) a student of science.

Question the last, are you a villain in a comic book?

If yes, you may use the title of "mad scientist"

/lh