Reply #59: I've experienced very different screening in the same circumstances

[14thColony]

A 'diplomatic bag' (aka diplomatic pouch) is immune to any form of search so long as it's properly marked as such and sealed. They can't even be x-rayed. I've traveled with a diplomatic bag through US and European airports; as soon as I produced my paper of exemption and my identification, that was the end of the discussion, even in the US and it was US gov property I was carrying. I did let a security person open the briefcase once and look at (but not touch) the sealed inner package, but I didn't even have to do that. And in those cases I didn't even have a diplomatic passport - the bag carries its own diplomatic immunity separate from the courier.

Even when it comes to the luggage of diplomats it's thin ice. The Vienna Convention on Diplomatic Relations (1961) says "the personal baggage of a diplomatic agent shall be exempt from inspection, unless there are serious grounds for presuming that it contains articles (that are considered contraband or are illegal in the host country - summary mine)". The US Dept of State asserts that luggage can be x-rayed and dog or machine-sniffed for bomb residue, but if something's suspicious it can only be opened and searched in the presence of the diplomat or an official national representative. I'd presume that if the diplomat refuses the inspection he'd be allowed to retrieve his luggage and depart the airport, but I'm not sure on that.