Read 1 Peter 4:4 Using Other Translations
Wherein they think it strange that ye run not with them to the same excess of riot, speaking evil of you:
With respect to this they are surprised when you do not join them in the same flood of debauchery, and they malign you;
Of course, your former friends are surprised when you no longer plunge into the flood of wild and destructive things they do. So they slander you.