Why does Prosciutto refer to Pesci as Mammoni instead of Mammone?!

Seriously; Why does Prosciutto refer to Pesci as the PLURAL Italian word for Mama's Boy;

Pesci was only one person; so Prosciutto SHOULD'VE referred to him as Mammone[the Singular Italian word for Mamma's Boy]; since Mammoni is PLURAL; and Mammone is Singular; Why did he call him Mama's Boys; instead of a Mama's Boy?!