Squirt isn’t lemonade, it’s a citrus soda. And also pee.
In the UK lemonade is a carbonated soda. I thought that was the root of the joke, with a cultural confusion. The other commenters seem to think it’s a pee joke? But if it was, it wasn’t funny so I think I’m right.
That said, my interpretation isn’t funny either? What is this post?
Citrus soda is lemonade in certain parts of the world. Australia for example.