Billingsgate (London)
.Gate = quay, and bellan is to bawl or bellow. This quay is so called from the shouting of the fishermen in trying to attract attention and vend their fish.
You are no better than a Billingsgate fish-fag, i.e. you are as rude and ill-mannered as the women of Billingsgate fish-market. The French say “Maubert” instead of Billingsgate, as Your compliments are like those of the Place Maubert, i.e. no compliments at all, but vulgar dirt-flinging. The “Place Maubert” has long been noted for its market.