Harry doesn’t talk to muggles or any one that is lower than him in significance. In the book, Rowling clearly shows how important Harry is; he only hangs out with Ron Weasely so others will see him as kind and caring, just to up his reputation. But really, hes in it for Hermione ;)
The boy in the robe shop (Draco Malfoy) bothered Harry because he was rude and stuck up. As well as soon as he saw Hagrid, he was rude to him and called him a 'servant' and a 'savage'.
