Fuddu means nonsense.
What a fuddu, he don't even know how to dance.
The Word Fuddu is generally used to describe a Dumb person whose actions make u hate yourself for befriending that person.
Basically, its a quality displayed by big time dumb, fools & retards...This is exactly like the word "Moron" just that it's in Hindi.
Abe Chal, Tu Toh Fuddu Hai