Best friends in the Harry Potter series, Daniel Radcliffe and Rupert Grint don't really like each other. Daniel gave an interview and says, “There’s this idea that Emma, Rupert and myself are the best of friends who always hang out together. I’m just going to put out there, Emma and I text all the time but Rupert and I never text each other, we never see each other. If I see him every six months or so, it’s a friendly ‘hello, how’s things with you’ but that’s about it.”
This could possibly be because Rupert is way more relaxed about life than Daniel and even Emma Watson. Daniel is just kind of strange to begin with and I don't think feels that comfortable in his own skin. Emma just wants to work 24/7 and Rupert just wants to enjoy the millions of dollars he made during the series and probably does not take the whole acting thing all that seriously and probably knows he got lucky with the whole red hair and age and casting.