How military kit & ridiculous supertanks got their informal names would make an interesting thread of its own. Indeed, 'Mammut' was the first 'nickname' given to the Pzkpfw VIII, with 'Mauschen' also reputedly preceding 'Maus'. The German military wasn't particularly prone to naming their vehicles at their conception, the Tiger & Panther began as PzKpw V & VI with no nickname (unlike the Brits, who tended to name everything in sight, including other nations vehicles - some of which stuck to the point being adopted by their progenitors - Lee/Grant, Sherman, Honey/Stuart etc) & tended to stick to an alphanumeric nomenclature, rather like the Americans (the Maus being either its VK prototype number or PzKpw VIII). It's quite likely that humourous nicknames were generally given by either the troops using a given piece of kit or the technicians working on their production somewhere down the development line.
Not funny I grant you, but quite interesting.