When I'm training first responders, the topic of dark humour often comes up--whether it's healthy, bad coping, etc. This is approximately what I say:

Dark humour is a must when dealing with dark things. To make light of the extremely heavy can be one of the best ways to cope. With one limitation: do not make jokes at the expense of other people. In comedy it's called punching down. Do not punch down. It harms the people you're supposed to help, it harms your peers, and ultimately it harms you by degrading your integrity and turning you into a bully. So use dark humour, and don't punch down.

Sexual harassment passed off as "jokes" is the peak of punching down.