I don't actually tell them to sod off. But, if I do get a US CBP employee that is being an arsehole over something then I will simply stop answering and ask for a supervisor. The vast majority of times the transactions are simple and straightforward, albeit usually unfriendly/cold and often what I call unprofessional, but as I said, I've only ever really had problems with US CBP officers as far as unnecessary questions or immigration staff playing the "respect my authoritah" games.