I wondered, on reading the chapter where he follows Harry to Quidditch practice, about Colin's obsession with Harry. And this lead me to form the following theory:

Colin has latched onto Harry as something to help him get through these massive changes in his world. From being the son of a milkman (working class, very real and grounded job) to being thrust into a boarding school for wizards (more middle class, obviously the opposite of grounded and normal), his haed must be spinning around madly.

I suspect that a famous young boy, who knows the Muggle World, and who is only a year older than Harry, would make a compelling and comforting figure to hold onto.

If all that makes sense.

Anyway. On this reading, Colin didn't bother me at all. In fact, if that's the case, then I'm really impressed by Rowling's understanding of human behaviour.