The antonyms for the word "be dressed in" are to be undressed, naked, or underdressed. Being undressed implies not wearing any clothes, while being naked means without any clothing at all. Underdressed, on the other hand, means wearing clothing that is insufficient for the occasion or not enough for the weather. These antonyms are often used interchangeably, depending on the context and the level of formality required. While being undressed or naked may be inappropriate in most situations, being underdressed can also result in awkwardness or discomfort, especially in formal events.