It was no Cannes do for Matthew McConaughey ... his new flick was booed in a big way at the French film festival.
A portion of the audience that screened McConaughey's film, "Sea of Trees" waited until the credits rolled to express their disdain and "booed loudly" according to "Variety."
Matt plays a guy who is distraught over his wife's death and tries to off himself in a forest near Mt. Fuji.
Some of the critics say it was unfair ... that the movie was good, but clearly not according to a chunk of the people who screened it.
Not surprisingly ... McConaughey kept his cool at a press conference for the film -- saying, "Anyone has as much right to boo as they do to ovate."
Remember .... a .300 average gets you in the Hall of Fame.