Something that went over my head as a child but just noticed rewatching this episode:

“There once was a man from Nantucket” is a famous opening line that is used in limericks.

As wikipedia simply puts it, “The protagonist in the obscene versions is typically portrayed as well-endowed and hypersexualized.The opening line is so well known that it, alone, has been used as a stand-alone joke, implying upcoming obscenities.”

So yeah. That’s why Mr. Simmons cut off Harold so abruptly. :D

ThE mOrE u KnOw~