When he was in the trenches in WWI, Hitler found that the ends of his moustache prevented his gas mask from making a good seal to his face. So the cut the ends until the mask fit, giving him the button moustache we are used to seeing.
I thought Hitler got his mustache from Charlie Chaplin.
It was a perfect fit in “The Great Dictator” (1940).
Legend has it, that during WWI, Hitler walked in front of British soldier, who refused to fire on Hitler.