Whats doin? Share definition Flag A slang greeting meaning hello or "Whats happening?" or "What are you up to?". Generally used among teenagers and young adults. "Whats doin?" "Not much, just work till 5. The boys and me are hitting the turps later though" Whats doin? by phenol red September 6, 2008 0 0 Get merch Get the Whats doin? mug. Buy Now — $32.95 See more merch