This is a famous saying popularized in the Roblox game "Guts and Blackpowder".
Experienced players
will usually shout this out in the online chat to signify that they have reached the end area of "Catacombes de
Paris" which is a map from guts and blackpowder. About the map, there is an NPC known as Jean-Louise-
le_petit-oui-oui-duboire (He's French). If you talk to the NPC it
will trigger the end wave and it
will spawn a bunch of zombies. They need to let the sappers of the team build barricades before talking to him so they
will be prepared once the horde comes. (The horde is only activated if you talk to him so if you stay out of his vicinity you could in theory never let the horde ever spawn).
French soldier 1 (A newbie): "We reached the end of the Catacombs! Oh who that guy, I'm gonna ask him for help!"
French soldier
2 (An experienced
player): "Wait no! Don't talk to jean!
French soldier 1 (A newbie): "What? Why?
French soldier 2 (An experienced player): "Talking to him
will trigger the horde, if we let the sappers build before talking to him we
will have barricades already set up."
French soldier 1 (A newbie): "Oh, ok i understand..."
French soldier 3 (
idk): *Talks to Jean either way*
Server: A votekill has been placed on French soldier 3.