Treat them as a child, until they grow up.
Or you do.
Try getting to know them really well, there might be a redeeming quality that could change the way you see them. This doesn't work all the time, of course. If they are truly infuriating, like how Spatial is to me for example, do your best to distance yourself from them because you'd most likely crack in the long run. There is no "have to" do anything after a certain age, including spending time with someone you dislike.