That guy who was laughed at the most during his homestay in America also came back to Japan speaking better English than anyone else.
この場合、次のような言い方ができますよ。
ーThat guy who was laughed at the most during his homestay in America also came back to Japan speaking better English than anyone else.
「アメリカでホームステイ中、一番笑われていたあの男性が誰よりも一番英語が上手に話せるようになって日本に帰ってきた」
to be laughed at で「笑われる」
ご参考まで！
カナダ 
