It would be quite hard for me to decide what kind of humor people at a workplace should have. But I might know a bit about how to make work a bit more fun.
So: Fun is all about being digital. Then you can send super-funny memes around and the entire IT support department will get it (that would be 2 people out of 100).
Ok I'm kidding, fun at work is not all about being digital and doing everything in a digital manner. I think digital should be treated like any other "channel" though.
Why are we so serious when it comes to writing stuff digitally? Is it because we know it's all saved and searchable (judging from peoples comments on Facebook, I doubt it)? Is it because when stuff is in writing, we feel that it's "final"? Is it because emails can be brought up as evidence in court and we've learned the hard way? Is it because it's very hard to identify sarcasm and irony in writing (see above when I tried to be ironic about fun and digital to the point that I had to write "I'm kidding")?
I'm not sure, but I think we need to loosen our digital communication up a bit. Try to write as you speak. It's harder when you don't have your body language, tone of voice and facial expressions to help you communicate, I know - but try it!
I think the people at Slack are great at this. When doing in-product copywriting, they encourage a looser form of language and I think that is needed in a lot of organisations today.
The new forms of communications at work also help us to have more fun and be more informal. Tools like text messaging and chat are very different from an email with your over-worked signature below it. Also, these "millennials" apparently use chat and texting quite a lot (I'm supposed to be a millennial myself, but I don't feel that young at all), so it's great if you'd like to attract them to your organisation.
What's not fun? Sexism. Racism. Bullying. All kinds of trying to put people down is not fun at work. It's actually not fun at all, so don't do that crap.
So since it's Friday - go grab a beer with your colleagues and later you can post some photos of yourself totally hammered on the company digital workplace tool. Or on Instagram, you decide.