Of course you're both right in a way, it's clearly kind of a regional thing-- personally I've been living in Asia for half my adult life so it's not surprising I mostly use the word 'kok' -- and I'm not alone: a quick search of this Hybrid forum will show 8,300 examples of people using the word 'kok'; 2,500 instances of people using the word 'hump', and only 526 instances of 'nuchal hump', even though as RD says English is the first language of most of us. On the other hand this isn't totally surprising, let's face it, it's the Asians who are the masters of creating and breeding this most coolest of fish...
All I can say though it's a good thing none of the people who used the word 'kok' 8,300 times were banned lol -- that would be cultural insensitivity/naivete
And call it whatever you want, my guy has a small one and he's proud of it!