The word 屁话 is formed through a vivid metaphorical combination: the first character 屁 means "fart", representing something worthless, offensive, and insubstantial, and it is directly attached to the second character 话, meaning "speech" or "words". The formation conceptually equates useless or irritating speech to the unpleasant, empty, and disregarded nature of flatulence, creating a single, potent term for "nonsense" or "bullshit" through this raw, sensory comparison.