that

英語のthatの使い方で、

I said that that that that that man wrote should have been underlined

の5個連続するのが最長と言われてるけど、

I said that that that that that 'that man' wrote should have been underlined

というように固有名としてのthat manを想定すれば6個もいけるんじゃないかと思う。