Agree the pace first
On the trail, the group sorts itself out once the pace is agreed. Before you start, set the pace of the person who walks more slowly and a point to regroup. The laughs come after, when nobody was left behind and nobody raced too far ahead.
The person who walks fastest is not the leader. They are the one who waits at the agreed point. If that is not said at the start, it gets said badly halfway, when someone is already tired and someone else is already far ahead.