A football team in the NFC composed of men who eat and shit green cheese. They also partake in man-on-man anal sodomy, resulting in the forcing of green shit in the rectal vault backwards into the sigmoid colon. The combination of eating cheese and having one's shit packed leads to severe constipation.
A phrase commonly used in World of Warcraft to tell players to avoid spells (like poison clouds, rain of fire, tail sweep and similar) that often deals massive damage to players and thus can cause a wipe.
This phrase apply to all kinds of harmful spells, even if they're not coloured green or coloured at all.
Encounter example:
The early boss Grobbulus in the raid-instance Naxxramas in WoW have the ability to put out green poison clouds under him. If the raidmembers stand in it they will die because of the damage.