Filthy Milkshake Share definition Flag When a girl has sex with more than one person within 24 hours so their sperm mixes like a milkshake. Doctor: "Who's the dad?"Person: "I'm not sure. I had a Filthy Milkshake." Filthy Milkshake by Your nan and her cat February 28, 2020 0 0 Get merch Get the Filthy Milkshake mug. Buy Now — $32.95 See more merch