Generally used to describe a situation where one persons faffing causes a series of faffs from several people, usually resulting in delay.
These faffs would most likely have not occured were it not for the initial faffer, therefore they have caused a faffalanche.
Person 1: "Taxi's here!"
Person 2: "Oh, hang on, im going to change my shirt"
Person 3: "I might change mine if you are"
Person 4: "Im going to use the toilet while you do that"
Person 5: "Im going to grab another beer then"
A faffalanche has been caused.
Person 2: "I might change my shirt"
Person 1: "Don't, the taxi's here and you'll cause a faffalanche"
A faffalanche has been prevented.