Parodied: People treat the random gibberings of a passing person as prophesy with no evidence or track record.
Zig Zagged: Mad Alice speaks in gibberish sentences which have some bearing on the current situation. Bob goes to her the next day and asks her to speak plainly. She gives clear, lucid advice which is entirely wrong. Her followers abandon her. Then she warns about a coming disaster, which everyone ignores. When the town is destroyed, she gives up and returns to gibberish... and gains a greater following than before.
Averted: A seer is otherwise an ordinary person.
Enforced: "If he were mentally stable then why wouldn't he just solve the crime himself?"
Lampshaded: "Why are all the good Seers loco?"
Invoked: The Oracle knows that to get taken seriously he will have to seem insane.
Defied: The Oracles of the world are carefully watched and given medical care to ensure that they don't become crazy.
Discussed: "The Oracle's predictions are always exactly what you need to hear. You just don't realize it until much later."
Conversed: "Just watch: by the end of the movie 'the blue cow mounts the red horse' will make perfect sense."
Deconstructed: The very fact that one can see the future alters the nature of their mindset, they become detached from humanity in a way that causes them to appear insane to other humans. They are in fact a different kind of sane, operating as they do on a different level of consciousness and are able to plan and communicate with each other with perfect clarity.
Reconstructed: The future is so nebulous and fluid that it defies attempts to speak of it clearly. Oracles speak in riddles and gibberish because it is the closest they can come to expressing it.