Kaiser Wilhelm II, pictured above, was jealous of Lord Kitchener's mustache. 'Pull my finger' he said on meeting our more than mortally hirsute hero at Bucking Palace . Kitchener, remembering that the querulous Kraut was the grand-son of Queen Victoria, reluctantly complied. But the Kaiser failed to reciprocate. This meant War.
Kitchener with his finger un-pulled, but still defiantly pointing (a posture he rigorously maintained till it resulted in his untimely death in 1916) is pictured below.