Also, avoid jokes that are mere rehashes of older jokes. The 12 politicians is a remake of “a hundred lawyers on the bottom of the ocean” from about 10 years ago.
Do you really not see the differences between “32 lawyers at the bottom of the ocean” and “12 politicians shot on the head”?? Let me spell some of them out for you:
Lawyers at the bottom of the ocean has an element of absurdity to it, which is what makes the joke funny (if in fact it is). Politicians being shot is something that can and does actually happen. Your version could easily be interpreted as urging an act of violence toward particular people, or as celebrating a recent event that most people agree was a horrifying tragedy
Offensive jokes are always in bad taste. Immediately after the precipitating event, they can only be told to the very narrow audience of those who revel in offensiveness, and those who hate the target group enough to approve of it. Eventually, the audience will expand to include those who revel in mere bad taste, and those who lack the empathy to be offended. Finally, such a joke’s popularity will plateau, as those who sort of enjoy feeling uncomfortable will give it a laugh.
Your joke, being (a) an obvious rip-off and (b) extremely topical, will never be that popular, as it’s got nothing going for it that will last past the first stage.
All jokes are fine if they seen for the humor. Jokes about recent events may evoke an emotional response to the actual event. Someone will be offended by any joke, but you can use common sense to determine if enough people will see the humor. If they groan though, just say ‘What? Too soon?’