Have a Lemon in the Honey Smile

What does Lemon in the Honey mean? Why it means bittersweet of course! The same as the term "beautiful ugly" used in the Caribbean (You'd call something "beautiful ugly" and means its wonderful but has its downsides as well).

I love this song and this is probably the best music video I've seen made for it. Can't help but feel wistful when I hear it ^^