Using Data Partitions, it is possible to restrict users from creating Requests, Incidents and Problems with oneself listed as the Affected End User.
This example can be created using Data Partitions. You'll need to create (or update an existing) partition with Type = create and Table = Call_Req.
The constraint will be as follows:
customer != @root.id
When linked to a specific role, this partition will prevent the related role from creating Requests/Incidents/Problems with the Affected End User equal to the currently logged in user.