a kettle of fish

For Simon, who wanted to know, from Brewers Dictionary of Phrase and Fable:

An old Border name for a kind of fete champetre or riverside picnic where a newly caught salmon is boiled and eaten. The discomfort of this sort of party may have led to the phrase 'a pretty kettle of fish', meaning an awkward state of affairs, a mess, or a muddle.

Probably not the context in which we used it at all, but what the?