It strikes me that there is an element of trust in humor. You certainly feel a lot more comfortable with humor at your expense if you have trust in the basic feelings of the speaker.

Imagine a "roast" given by the people at your workplace with you as the guest of honor. Your friends start picking on your foibles, i.e. you dress flashy or you dress really casual; you throw your money around or you are a tightwad; you keep your car looking shiny and clean all year round or you drive a beat up old thing; as long as these are people you like and trust, sure you may squirm a bit but all in all you will feel pretty good about the humor. The next person who gets up to speak in the guy you think may be after your job. You suspect he is trying to take credit for some of your work and to pass blame for some of his failures onto you. He makes some jokes at your expense, maybe about your desk, it is very neat or it is very cluttered, and people laugh. All of a sudden, the feeling you have changes from a mixture of fun and maybe mild embarrassment to one of anger. Why? I suspect it is because you don't trust his motives. It feels wrong that he should hold you up for ridicule.

I think a common mistake that it is very easy to make is to assume a stronger sense of community identity and group bonding than truly exists. The illusion of trust can evaporate quickly when someone hits on a sensitive topic and there is not enough trust to support the strain.

Sourdough (who trusts you will not throw bricks - or even epithets)