The astronauts have a sense of humor. Does that surprise
anyone? There are many instances where they played practical jokes on each
other. Was it to have fun? To relieve stress? To break the tension? Well, you
would have to ask them.
One example of the types of practical jokes the astronauts played on each other during the Apollo Era was the Apollo 14 "Roadrunner" or BEEP BEEP Patch.
There are many accounts of the story behind the patch that are detailed in different books such as, "The Last on the Moon" by Gene Cernan, but the basic tale is that the Apollo 14 backup crew used this patch to drive the Apollo 14 prime crew towards their goal of landing on the Moon.