The Bet (1997) on Netflix

Plot summary

Bernard teaches in the suburbs and shares a home with Victoria. Didier is a pharmacist in Paris, married to Victoria's sister Murielle, and he drives a black Mercedes while Bernard's car is old and rusted. The two brothers-in-law are opposites and cannot stand each other. At a family dinner they make a bet: each will give up cigarettes for fifteen days, until the family next gathers. The first days pass easily and both men feel pleased with themselves. Then the craving grows. Bernard and Didier turn irritable, suspicious and untruthful, and the wager begins to weigh on their work and their home lives.