If you're one of those Scrooges who thinks it's weird to give a Christmas tip to the mailman, remember this:  HE'S MISERABLE.  According to a study by the website MyPlan.com, postal workers are THE most miserable workers in the U.S.  Only 25% said they're satisfied with their jobs.

The happiest workers in the U.S. are, randomly enough, SINGERS.  91.7% of people who make a living singing say they're satisfied with their jobs.  The five happiest workers are singers, firefighters, aircraft assemblers, pediatricians, and college professors in communications.

The five most miserable workers are postal workers, program directors, municipal clerks, food prep and serving workers, and maids and housekeepers. 

(Yahoo Finance) 

Check out various lists of happy and unhappy workers here.