In general the answer to this question is “Oui,” “Si,” “Ja,” “Hai,” or whatever means “Yes” in the diplomat’s home country. A registered diplomatic agent (and his or her immediate family) gets full immunity from the criminal and civil prosecution for DUIs in the U.S. An embassy or consular employee gets similar immunity but only if the offending acts were committed as part of, or during their official duties. For example, a Russian attaché who allegedly struck a police office while driving drunk managed to avoid charges by claiming diplomatic immunity. However, a Mexican consular employee was arrested could not claim immunity with a .126 BAC in Georgia in 2012 (traveling 91 mph in a 65 mph zone) because the incident was not connected to official duties. (The consular employee was arrested, and in a plea deal, was sentenced to 24 hours of jail time, probation, fines and community service.)
The principles behind diplomatic immunity are threefold: First, foreign diplomats do not always understand the laws of their host country. Second, diplomats should be free of legal harassment in the host country. Third, the concept is based on mutuality and a concern that punishment of a diplomat in a host country will trigger retribution against U.S. diplomats in the diplomat’s home country. On that basis, foreign diplomats in the U.S. are granted varying degrees of immunity from prosecution for certain criminal and civil prosecution. Note: in egregious cases, home countries often step in and discipline the diplomat or charge the diplomats with crimes in the home country. (Of course, diplomats in their home countries are not excused from DUI laws.)
The hubris of diplomats often leads to abuses of legal immunity particularly in regard to driving laws. One notable example is with parking tickets. Two cities with diplomats – Washington D.C., and New York -- have sought federal legislation created a “parking ticket exemption” for diplomatic immunity. (New York City, alone, claimed over $16 million in unpaid parking tickets.)
In the U.S., the rights of foreign diplomats are derived from the Diplomatic Relations Act of 1978 and based on international treaties. At it highest level, a diplomat with full immunity can shield himself or herself (and their immediate families) from all criminal prosecution including the worst consequences of a DUI. The U.S. provides several levels of immunity to diplomats. In general these are:
A diplomatic agent with full immunity cannot be sued in a civil lawsuit in the U.S. The inability to chase diplomats via civil suits can hinder families of victims of DUIs. For example, the civil debts alone from foreign diplomats claiming immunity in the U.S. amount to somewhere between 5.3 and 7 million dollars (most of it attributable to a failure to pay rent for office space).
Note, in some cases, diplomatic immunity extends beyond diplomats to the employees and members of international organizations (a power derived from the International Organizations Immunities Act.) For example, it was under the power of the latter law that Dominique Strauss Kahn, sought, but failed to obtain immunity from a civil suit charging sexual assault. And of course, immunity will never extend to those who falsely claim to be related to diplomats.