I once took out a library book which was an analysis of humour.
About halfway through, I came to the conclusion that either I didn't understand the analysis or that the author didn't understand humour.
Possibly both.

Anyone who thought that the Anne Frank joke wasn't in good taste would be well advised to NEVER join the Royal Navy. The standard comment in that service, when someone is killed or maimed, is 'He shouldn't have joined if he can't take a joke!'
As several have commented, humour is sometimes a coping mechanism.
And totally subjective.