The common excuse for using an extra of ("Get off of that!") is that it's a regional usage. That excuse is not acceptable to the King. That extraneous of is ugly and grating, and all ugly and grating regional usages are being steadily eliminated from Anglophonia by the Royal Enthusiastic Thug Platoon.
The non-regional alternates sound much better: Get off instead of get off of. Behind instead of in back of. Out the window instead of out of the window. And so on.
Were I but King of Anglophonia
Of Off and Of