Here is Urban Dictionary's definition of flid:
A widely used insult in England, i dont know about America its probably there too. It is quite an extreme insult, most people dont like it (obviously), means spasticated or retarded.
It comes from the German drug* that was used in the 60's to help calm the side effects of pregnancy, but sometimes caused physical abnormalities in the baby. A flid is actually originally a person with no arms and legs.

And here is a trailer for the upcoming film, Kung Fu Flid:



Horribly offensive? You bet.
Horribly entertaining? Ditto.

* Note: That drug is Thalidomide.