Porteño Spanish is the dialect of caste-sha-no (castellano) spoken in Buenos Aires, Argentina and the surrounding areas. It is categorized by an Italian-like pronunciation and colorful Lunfardo slang.Browse Slang Dictionary
Forro literally means lining or cover, but os used more often to to refer to condoms.
It can also be used to describe a rude or unpleasant person. For instance "ese tipo es un forro" means "that guy is such a prick".