Read in yesterday’s Guardian:
Ned Sherrin, wit, impresario, bon viveur and Radio 4 Stalwart, dies at 76.
The Compact Oxford English dictionary tells us that bon viveur is another term for bon vivant.
ORIGIN pseudo-French, from French bon good’ and viveur a living person’
This isn’t quite right. In French, a viveur is someone who lives for pleasure and leads a life of debauchery; it has negative connotations and I’ve never seen it attached to bon. A bon vivant (vivant being the exact word for "a living person") is someone who enjoys life and its pleasures, particularly food and drink, which was apparently Ned Sherrin’s case, as I then heard later on Radio 4, in a piece where bon viveur was also used to describe him. I don’t think these two expressions can be used as if they were interchangeable, because in French they describe two very different people. After all, it would be unfair to suggest that someone who simply likes the odd tipple in good company is in fact the kind of person who rarely emerges before three in the afternoon and is at their happiest lying face down in the gutter having just drunk the entire contents of the local supermarket’s alcohol aisle.