I think that "les parasites" is a hypocritical movie. Worse, it's a movie that doesn't focus on the main topic at all. However, the title of the movie is sufficient enough to draw the attention to the movie. You expect to see a place and a precise time (here it happens to be a New Year's Eve party) turned upside down by a band of parasites. Such a topic would have demanded a caustic and malicious humor.
Well, at the end you're far short of the target. This New Year's Eve party is eventually like the ones you know. It means with slight rows from certain guests and without any major incidents. Moreover, you can't really say that they are parasites through and through because they don't mean to spoil a party and we even can't define who they are.
Apart from this, "les parasites" is a muddle-headed and unfinished movie. Its screenplay is labored and doesn't avoid a quite important number of stereotypes. Some abortive situations with vain dialogs and, by moments, a crude humor don't save this movie from mediocrity, neither the excessive play of nearly all the actors.