Humour is a great tool across the board and game design is no exception. It won't carry a game on its own, but it can go a long way towards making a good experience great. It's also a fantastically volatile tool, if it doesn't work at best it's a little embarrassing, at worst it's outright offensive. Doing it badly can utterly sour what might otherwise be an enjoyable experience. Yet trying to get it right is also undeniably attractive, when I found out just how far musicians go in mocking each others foibles my first reaction wasn't "Better tread carefully and keep that out of the game". It was "Fantastic, that's going in!"
So far playtesting is going pretty well. All of the instrumentalists I've played it with so far have got something out of the theme and players who don't get the references don't find that they detract. It took a bit of trial and error to get to that stage, but over the course of the games development I've found myself with an informal list of rule for taking the piss (though the medium of boardgames)
1) Don't say anything with a game you wouldn't say to someone's face
You can delete the line "with a game" and this is pretty much a good rule for life. If I want to say something in a game I imagine saying it to someone's face and see how I feel about that. I wouldn't include the card 'Troublemaking Trombonist' if I wasn't willing to walk up to a trombonist and say "I hear you guys are traditionally the devious ones, what's the best caper you've pulled?" Perhaps that's low hanging fruit for me because I admire troublemakers, but the point stands.
2) Never punch down
It's a classic rule for comedy and it applies to games as much as it does to any art form. It's generally better to find humour at the expense of people with more social standing. Not only is it less likely that you're going to tell a joke that amounts to "Ha, your life sucks, isn't it funny how much you suck?" but it also tends to help you avoid the lazy easy stuff.
This isn't a huge problem with orchestras, since they're traditionally composed of people who are doing well enough to own an expensive instrument and have time to practice it, but it did make me shy away from the easy targets. When I heard my first viola joke I thought that maybe there needed to be a card mocking violists, when I heard my fiftieth I knew that what I really needed was one mocking common attitudes about violists.
3) It's better to mock people for being awesome
The best joke at someone's expense is one that they can join in with wholeheartedly. I'm not talking about the thing where someone joins in laughing at themselves because the room is doing it and they want to feel included but will cry themselves to sleep about it later. I mean the thing where the truth behind what you're saying is a fundamentally good truth that someone can be proud of.
I guess I'm basically recommending the backhanded compliment. For life in general the out and out regular compliment is preferable, but in games there's a place for hyperbole about positive traits. It's hard to get offended by the notion that your face is so damn beautiful that the orc will take a called shot penalty not to risk harming it. Not least because it comes with an appropriate mechanical benefit! But obviously this only works if the positive aspect is true, otherwise it comes across as sarcastic.
4) Assume you're not funny
This is a really good assumption for me, because I'm usually not. However even if you are hilarious, it's good to look at your work and question what it's like if you don't find it funny. Humour varies dramatically from person to person and what'll tickle one person will have absolutely no effect on another. So at least some number of people will look at what you've done and see it stripped bare.
It's good practice to look at your things in that light, but it's especially true of games. There are a lot of games that when you strip their coating away, there's nothing underneath. If you're not amused by their theme then they'll utterly fail to entertain you in any other way. I think that it's important for a game to be a game.
5) Weaponise rarely and consciously
You can break all of the rules and go for the sorts of thing that'll hurt people. I don't think it's something that should be done often or by accident, but I feel the need to wrap up this article but acknowledging that meanspirited humour has a place.
Part of being human makes us laugh in the face of death. So much so that it's a familiar phrase. When we find something so awful that we can't easily comprehend it, there's a tendency to laugh. I think that's healthy and I reckon it's good for us. I think it generally has more of a place about the great unstoppable forces of creation than individuals, but when an individual or group become a cause of great suffering then that seems like fair game.
This is broadly hypothetical for me, I've not made a game that's purpose is to lash out in this way (Though I suppose with the current state of British politics I've got something of a target rich environment.) Every game I've played of this type also tends to have some social message that got into the creators brain so strongly it caused them to utterly forget to actually make a game and so winded up being some appalling piece of garbage.
Still, I think there exists some space for a game that holds up excellently as a game and finds the right balance of viciousness, directed in a way that compliments its mechanics and enhances the whole experience.
Then again, maybe it's been around for years, but is too subtle and nobody gets the joke