It has been said that the most stressful part of being an astronaut is finding out if you've passed the training or if you got a flight assignment.
Seriously, though, training to be an astronaut is a textbook on how to cook up stressful situations. They undergo survival training, e.g., learning how not to die in hazardous situations, how to maneuver in space, weightlessness, and worse.
Stress can also arise from dealing with fellow human beings on the mission: body odor, boredom in an environment when even simple things become difficult—like elimination, eating and grabbing at weird things floating through the air.
But hey, astronauts are supposed to deal with stress better than mere mortals. That's one of the things aspiring astronauts are tested on. And one way to deal with the stress that comes from space station crew mates driving you crazy? Take it out on Mission Control. Houston—you have a problem.