'Bird feather' literally, but in colloquial Mandarin, 鸟毛 (diǎo máo) is a highly informal, vulgar slang noun meaning 'nonsense', 'rubbish', or 'bullshit'. The term derives from the homophonic and taboo use of 鸟 (diǎo), which sounds like a coarse euphemism for 'penis' — similar to English uses of 'cock' or 'dick' in expressions like 'cockamamie'. Combined with 毛 (máo, 'hair/feather'), it forms a dismissive, contemptuous compound implying something trivial, worthless, or utterly absurd.

This expression is strongly associated with male-dominated, casual speech — commonly heard among friends, in online forums, or in heated arguments. It carries significant informality and mild offensiveness; never use it in formal writing, professional settings, or with elders or superiors. While not as extreme as some four-character profanities, its tone is blunt and irreverent, often conveying frustration, mockery, or emphatic rejection of an idea or claim.