Friendships can operate under a lot of different rules. What's okay for one set of friends can be unthinkable for others. So it's often not for us to judge whether or not a friend is being offensive to his/her friends, since we're not familiar with the social rules within that group.
However, I'm pretty sure that if you say someone should be wiped off the map, that makes them your enemy, not your friend. Of course, no one told the Iranians that.
Iran: Calling for Israel's destruction in a friendly manner, since 1979.