1. A urn-like vessel for gathering, storing and processing a culmination of various excretions (including, but not limited to, semen, sweat, vaginal secretions, lubricant remnants, blood, saliva, pubic hair, other waste product) derived from the execution of a sex act. Although a definite insult, perhaps the more insulting is the “fuck bucket worker” – cursed to spend her/his time removing the residue of others with a sponge attached to a pole. Then squeezing the substances out of the sponge into the bucket.
2. An insult suggesting that someone is as useful as a bucket full of the above substances.
As a general explicative similar to "damn": "Elaborate Japanese fuck bucket!" (I image nice pictures and elaborate details all around the urn-like vessel).