professional student
Person who receives multiple degrees and keeps taking courses instead of holding a profession related to the degrees earned.  Can be a compliment or an insult depending on the speaker.
Ex. 1: a compliment
"Man, I think you're so cool for writing a dissertation on Mesoamerican maize fertilization.  You're a real professional student!"

Ex.2 an insult:
"Hey Jack, won't you get a real job and quit being a professional student?"