Grocery Grammar

Shopping in my local greengrocer's yesterday, I overheard two of the staff talking. One called the other a lummox - apt, sure enough, but not the kind of word you hear bandied around in effing and blinding South Bristol. Even more unusually, rather than follow up this insult with an expletive laden riposte, the recipient instead questioned whether lummox was singular or plural. He thought the latter, and argued that the correct usage in this case was therefore lummock. His friend disagreed, contesting that a lummox multiplied was a group of lummoxes. I was chuckling to myself so much that I nearly missed the bag I was placing my tomatoes into. What a lummox.