From the obituary of Roger Hall:
One of his favorite OSS stories involved a colleague sent to occupied France to destroy a seemingly impenetrable German tank at a key crossroads. The French resistance found that grenades were no use.
The OSS man, fluent in German and dressed like a French peasant, walked up to the tank and yelled, "Mail!"
The lid opened, and in went two grenades.
Click through to read how Hall handled the surrender of a German colonel. Via.
Here's a longer obituary in the NY Times, which convinced me to add Hall's book You're Stepping on My Cloak and Dagger to my Amazon wish list.