The joke explained repeatedly has begun asking the audience to do its work.

A joke that needs explaining has moved the labour onto the listener. Instead of arriving whole it now comes with instructions, and the laugh it collects is politeness rather than surprise. Explaining does not repair it; it changes what the thing is. Timing and shared reference are most of the machinery.

When you catch yourself explaining, let it go rather than pushing harder. Notice whether the room shares the reference the joke depends on, since that is useful information about the room. The same holds for ideas that need too much scaffolding to land.