The point is not that you need to know the recipient, but that if you don’t know them you can’t say if they will enjoy this kind of humour or not.

I know people for whom such a letter would be the highlight of their day. I know people who would be worried about it for days if not weeks. Without knowing your audience you can’t know who will react how.

> Is it worth the risk that someone would find it "incredibly bad taste" (parent post, not yours)?

Is it? Depends on how much you care how much you care about being an asshole accidentally.

I have friends who we play pranks on each other where we sneak up on the other and do a jumpscare. Would never do the same with a random person though.

This is the equivalent action, but instead of threatening people with bodily harm it is threatening them in a legal/bureaucratic way.

> Obviously humour is subjective

Yes.

> perhaps such people need to have their Sense of Humour shifted, Overton-window style

Or maybe your sense of empathy needs adjusting. The problem is not with their sense of humour but with their sense of “how likely it is that an official looking letter is bringing ruin on me”. I’m glad that you feel secure enough that you can’t even understand that feeling.