Tronches is not quite French slang, more a colloquial word for face. It translate to 'mug' as in mugshot.
When i first saw Tronches de Vin mentionned, I thought it would feature portraits of winemakers.
Actually this book written by 5 French wine bloggers is the anti-establishment version of a wine guide.
They call it an 'anti wine guide'.
It will be published in France in March 2013.
(* Image from 'Tronches de Vin' Facebook page)