what is a whipperdee

Without the context in which the term was used it is difficult to determine. 

A "whipper-snapper" is a young person or a presumptuous person. 

A "whippoorwill" is a N. American bird.

And a "whippet" is a breed of small fast dog.

Possibly a derogatory remark that is a variation on one of the above?

(a) A large sting ray (Dasybatis, or Trygon, Sayi) native of the
Southern United States. It is destitute of large spines on the body
and tail. (b) A large sting ray (Rhinoptera bonasus, or R. quadriloba)
of the Atlantic coast of the United States. Its snout appears to be
four-lobed when viewed in front, whence it is also called cow-nosed
ray.

or

CancerWEB's On-line Medical Dictionary