I think that the term bullying is very overused, probably because it's the easiest way to express a view on a particular situation. I think Nigel is a verbal bully, in the way that he immediately shuts Lembit down as soon as he opens his mouth. If Nigel was giving Lembit a physical slap every time he said something, it would be much easier to define. Nigel was annoyed that Lembit likes sour food, because he hates Lembit. No other reason. So he just had to jump all over him. Also, Nigel's behaviour seems to be an acceptable norm these days. Hatred breeds irrationality.