drille : nm The word drill, whose etymology is controversial, appears in 1628 in military slang. He first designates a vagabond soldier, a soldier who does not hesitate to provide himself with drink et food, more or less force, at the inhabitant.
The expression "of merry drilles": happy and sympathetic companions.
Probably because these "drills" were often revelers, that they were good companions among themselves who supported each other in their bad actions as well as in their drinking bouts and other groupsex, there remains, despite the initial negative side of their behavior, an image of camaraderie that has endured until now.
We once had the right ones et the bad guys, but now we only have the merry kids, roughly synonymous with happy boys, and, more rarely, the old guys, more specialized phrase to designate libertines.