Most Helpful Guy
If he's a bad person then do it over phone call, text, facebook, instagram, etc. However, if he didn't do anything wrong then its very disrespectful.
Most Helpful Girl
Yes And... Tacky here, dear.
Face to face is always the best way to go. If you have been these two birds of a feather for a long time or even dating awhile, then tell them to their Face so you can end the madness and you both can move on.
However, if you feel you cannot Face them, call them up and tell them with no hymning and hawing and less squawking.
Good luck. xx