An invitational screening of a film has just ended, and you, a journalist, were not a fan. (You wanted to be, but the film wouldn’t let you.) And now you’re on your way to the after-party.
The general etiquette is as follows: (1) The journo is obliged to be as fawning and gracious and complimentary as possible when speaking to talent or studio reps, although he/she is not obliged to lie outright about his/her reaction to the film in question; and (2) It is permissible for journos to mutter their true opinion of the film with colleagues if they happen to be out of earshot of talent or studio reps.
Case in point: “Ringo Starr’s ‘The No-No Song'”, posted on 8.28.16.