jomamma Share definition Flag Originated in about 1983. From a Knock knock joke. About the time (your mamma) jokes started. It was in place of YO short for YOUR. Hence JO Knock Knock...Who's there? Jo.. Jo Who? JOMAMMA. jomamma by jomamma2 February 7, 2010 0 0 Get merch Get the jomamma mug. Buy Now — $32.95 See more merch