The term "brown-nosing" is often associated with flattery or obsequiousness, but there are plenty of antonyms that represent the exact opposite. Some potential antonyms could include forthrightness, outspokenness, frankness, honesty, and directness. These words all suggest an individual who is unafraid to speak their mind and who does not engage in flattery or excessive praise. Other possible antonyms might include skepticism, cynicism, or even apathy, as these words reflect a lack of interest in sucking up to authority figures. Ultimately, it is up to the individual speaker to choose the appropriate antonym based on the context of the conversation and the intended meaning they wish to convey.