Generally the exploreres get to name it. There are a few "conventions":
Don't name after living people, especilally yourself (unless its a good 'joke name' like Elbons Kram").
Don't whatever you do, name it after your girlfriend (eg. Samanthas Passage) or you will be ridiculed.
Don't "overname", i.e. don't give names to every 2m of passage.
Don't use abusive names
Example from our project are:
Huge Crawl: Its squalid and tiny.
Wotno Streamway: It doens't have a stream in it
Rising Damp: A sump that rises and falls....
The Tourist Trap: A tight squeeze that a 'guest' digger got a bit stuck in....
Floodgate Pot: Don't be below it if it rains...