But inappropriate != illegal. The union of what each person considers socially inappropriate is a rather large set... both undesirable and impossible to legally enforce. As other comments say, there are better things to be upset at here.
There are a lot of reasons to get upset in this world, and a lot of things to get upset at. If this is something sensitive to you for personal reasons, I get it. Otherwise, you should probably just accept that people aren't going to always conform to your view of perfection.
I joke all the time with my family and friends that I'll kill them if they ever repeat something I say in confidence. It's tongue in cheek, an obvious over-exaggeration, and often used for humor.
There's certainly nothing wrong with trying to be kind. however, this is an interesting issue because I see the desire to force other people to conform to your beliefs a form of bullying.
I suppose it depends on where you place the responsibility of offense. Should everyone be (socially) required to consider the feelings of everyone around them before they say anything? Or should people learn to accept that others won't have their same experiences and values, and in that sense, "grow a thicker skin"?
Put more succinctly, is offense given, or is it taken?
If I made the same joke behind his back, but still without any wish for him to die... is it suddenly bad? Arrest me!