On what makes a film genuinely funny rather than competently funny.

Competent film comedy works through recognizable mechanisms: setup and punchline, incongruity, escalation, the violation of expectation. You can analyze why a joke is working and your analysis will be correct. The joke remains funny anyway.

Genuine film comedy does something different. It creates a world with its own internal logic and then follows that logic to conclusions that are funny because they are true rather than because they are incongruous. The best Coen Brothers comedies work this way. Raising Arizona is funny because the film has committed fully to a vision of Arizona-desert-trash-culture that produces its jokes as natural consequences rather than setups.

The same distinction exists within horror-comedy: films that are funny and scary because the scariness and the funniness are the same thing, not alternating registers. An American Werewolf in London achieves this. Tucker and Dale vs Evil achieves this. What they have in common is total commitment to the internal logic of their premises.

The most reliable sign of a genuinely funny film is that you cannot find the seams. The jokes don't feel placed. They feel inevitable.