An example of suing a diplomat/state without foreign policy considerations: an Indian diplomat was sued for underpaying her domestic help. In response, India promptly sued spouses of American diplomats for tax evasion, illegal imports and fraud.

Quoting from https://en.m.wikipedia.org/wiki/Devyani_Khobragade_incident

"Former Finance Minister Yashwant Sinha called for the arrest of same-sex companions of US diplomats, citing the Supreme Court of India's recent upholding of Section 377 of the Indian Penal Code.[72][73] The Indian government asked US consular officers posted in India to return all identity cards.[7][6]

On December 17, 2013, Delhi Police removed security barricades on the road outside the US Embassy in New Delhi, citing need for improvement of traffic flow in that area.[74] India has demanded an unconditional apology from the US government[74] and asked the details of the salaries of all domestic help, gardeners and other staff employed by US consulates in India to check for inconsistency or frauds.[74] India moved to block perks such as alcohol and food imports at concessional rates, for embassy employees.[75] With new restrictions, U.S. Embassy Vehicles will not be immune to traffic violations, the restrictions also requires the embassy not to hold 'Commercial Activities' in its premises.[76] Indian income tax and immigration authorities are investigating allegations of work-permit, visa and income tax fraud at the American Embassy School.[77][78][79]"