Ian over at Forgotten Weapons got his seemingly giant hands on a tiny .167 caliber Menz Liliput pistol, which is only slightly more dangerous than a good sized rock. Maybe.
From the late 19th Century up until the cusp of World War II, Europe was awash with guns so small they seem like novelty cigarette lighters. This wave included the bite-sized Velo Dog series revolvers and transitioned to semi-autos such as the Liliput, which dates from the 1920s.
Yes, this is a real gun and, best yet, you could probably conceal it in a handlebar mustache.