pickknow one's onions . know one's onions {v.} To be well acquainted with a subject. Categories: add yours British verb Source: British slang (Wikipedia) 'know one's onions' on video KNOW ONE'S ONIONS Detention - Know One's Onions {NYH114} Know One's Onions BlackBerry App «FFXI-Movie» #0100 - Know One's Onions sort: relevance, mode: exact match, q: "know one's onions", maxResults: 4, videoEmbeddable: true, videoSyndicated: true, safeSearch: strict, type: video Subscribe to: British SlangEnglish Slang Leave my opinion