crackpot

This term carries a strong derogatory connotation, suggesting that a person's ideas are not just unconventional, but fundamentally irrational or delusional. It is typically used in informal contexts to dismiss someone as being beyond reasonable argument. When used as an adjective, it often describes theories or schemes that are perceived as wildly unrealistic or scientifically unsound. It implies a lack of grounding in reality, often bordering on the absurd.