We can say to him/her that to change him/her attitude . We can explain to them that when we are rude to others, people will not want to be friends with them. They will not want to  go near them and then they will no friends to  help them out in their difficulties.If they change their attitude and instead be good ,kindhaerted and sharing every one will rush to become frieds with them.
If at all we have a friend who is not well-mannered or say rude and arrogant then we need to first speak  to him/her about the importance of being kind and polite.Our lives should be as an example for him/her,and we need to slowly start helping him/her with the difficulties he's facing.But the most important thing is that we need to find out the reason behind his rude behaiviour  cause children usually  who are very poor,who feel inferior of themselves  or who belong to broken families behave in that way.