Fujoshi is a term mostly used for yaoi fangirls ,it means "rotten girl".
Fudanshi means "rotten boy"
Fudanshi is a boy who likes yaoi (boys love).
Sometimes it might be used to describe someone who likes to pair up characters in animes and mangas.
Ex.:(Haruno Sakura x Sai,Zoro x Robin).
That fudanshi paired up Lucy and Loki.