A combination of the emoticon D: and the physician tittle Dr
The 'r' can also be seen as a headlamp.
Sources of stress includes massive amount of knowledge to to memorize in a short amount of time, working over 60 hours a week during residency, crazy requirements and selection of medical school and the combination of the lack of sleep and high consumption of caffeine/energy drinks.
Med student 1: We have our Unit 2 exam next week.
Med student 2: D:r