the little boy in the comic book store was named Keith Nash. His name was mentioned 3 or 4 times for some reason... not just "Keith", but "Keith Nash". Was it a reference to something? An inside joke by the writers?
Its possibly because, in Britain (the creative home of this movie) it is more usual, when asked your name, to respond with your christian name only (this isnt a rule or some sort of etiquette). My take on this is that because the character responded with his full name, Paul was gently making fun of him.
As I see it, Paul asked the boy in the comic store his name and, like most youngsters of that age, he gave his full name, ie "Keith Nash".
Paul then said, "Hello Keith Nash" in a sort of avuncular way that most adults do when children unneccesarily give their full name in response to such a question.
The "joke" therefore is - when Paul says the boy's full name a second time Paul and the rest were in the RV being threatened by the agent with a gun. Just before the agent is about to shoot, a child appears as if from nowhere, and seems to hit the agent for no reason (as far as Graeme was concerned, as he had not seen the child before). Graeme naturally said words to the effect of, "Who is that?" in the sense of "What the hell just happened?". But Paul happened to know the boy's name and could cheekily answer, "It's Keith Nash" giving Graeme the false impression that the boy is well known and his name should be widely known by all.
A fairly simple joke made even less interesting by this expanation!
Perhaps similar to a joke in The Naked Gun (1988) where Frank Drebin by chance takes over the role of a singer named Enrico Pallazzo who is due to sing the National Anthem at a baseball match (so Drebin can get closer to the players and look for the bad guy). Unfortunately Drebin is cornered into singing before he can duck away to search. He sings badly to the disgust of the crowd. Later he is a ref behind the plate, finds the bad guy, people want to know who was the hero, Drebin takes off his mask and (instead of people recognising him as Drebin) someone calls from the crowd, "It's Enrico Pallazzo!" Yucks all round.
I think the average kid, when asked his name, would give his first name only.
The name is repeated twice by Paul, once during their introduction and once when they are making their getaway in the RV. And in that instance there was no reason to even say the boy's name. Someone says 'Who's that kid" and Paul's response "Keith Nash". Serves no point, does not move the plot forward.
Keith Nash is a name that Simon Peggy and Nick Frost thought was funny.
From an interview on About.com: Simon Pegg: No. We just like the name Keith Nash. We just thought it was a funny name. Well, its not a funny name, its an ordinary name and had some comic value.
I think there is an unspoken reason(within the film) as to why Paul repeats the kid's name and that is...
Paul has spent sixty+ years as a "guest" of the US government and also tends to get unfavorable responses to his existence from any humans he's met. And, there he is running into some random kid in the store who, not only doesn't freak out, but is actually really friendly with him(for the short time they talked anyway). Paul is kind of inspired by that and then he becomes doubly inspired by the fact that the kid, whom he'd only just met, came to his rescue by stopping the agent who's shooting at them. So, when Graeme incredulously asks "Who's that kid!?", he responds with "Kevin Nash!" in a 'I'm proud I know him' kind of way. ;D
I would like, if I may, to take you on a strange journey.
I love how people on IMDB take a meaningless piece of throwaway dialogue and turn it into something deep and philosophical- as the director and screenwriter most likely never intended.