It is a hard one as arrogant people aren't nice. No one likes arrogance and normally the person doesn't know they are arrogant lol.
The best way is to learn the hard way and be honest with the person. Hurt their feelings if you have to and bring them down a peg. If it rocks them then it is good. Tough love is the hardest love and an arrogant person needs tough love and hear the truth. This may work depending how arrogant they are as they don't like to hear the truth.