when the coiffure of a young man (preferably of jewish descent and who has thick wavy hair) is cut on the sides, giving the impression of a cross between the top fin of a fish and a mohican-style hair cut, hence the compound "fish-hawk." can be used to describe the hair do or, more often, the person wearing the hair do.
"did you see his new haircut? it's totally a fish-hawk"
as a nickname:
"yo, fish-hawk, do you want to study french and drink tonight?"
(yelled) "FISH-HAWK!" (from across a long distance)