Watson: Sherlock, where do lemons come from?

Perfect dad joke. Made me groan-laugh. I’d make it more obvious by changing it to: “A lemon tree, my dear Watson.”

It's this supposed to be a dad joke as an anti joke?

I had a similar joke: Watson: I say Sherlock, why did you put that lemon in your ass? Sherlock: Lemon entry my dear Watson.