Not clutching my pearls but...
I have never seen a movie that contained so much filthy language.
I have seen this movie advertised as a comedy, but I don't think there was a single moment that made me laugh. I found it by turns touching and horrifying,
I empathized with Ms. Hayes, and even understood how she felt to an extent, but her anger and vengeance were so extreme that she had no empathy for the dying Willoughby, even though he did his best to explain why there had been no progress made on finding her daughter's killer and expressed his compassion for her. She didn't even think of the effect on her son of her actions. It does seem that her demands for vengeance for her daughter are in part motivated by her own guilt over her last interactions with her daughter Angela, in which echoing Angela's words she says she hopes she is raped, and that is what happened.
In the previews the clips used were amusing but not when seen in context.
I guess all of the actions taken by Dixon and Ms. Hayes were meant to be funny as they were so outrageous, but I did not see them that way.
It was a good movie and the lead actors were convincing in their roles. Frances McDormand was believable as the exhausted grieving mother making a sort of memorial to her daughter near the billboards. Her scene with the deer that wandered into the scene was touching. Sam Rockwell allowing a possible rapist to beat the daylights out of him to get the rapist's DNA hoping that it might lead to Angela's killer is another poignant moment and a complete turnaround for his character. Peter Dinklage as the barkeep who bravely ran out to rescue Dixon on fire and in spite of having seen what happened, provided an alibi for Ms. Hayes, asking only that she allow him to take her to dinner was convincing in his comportment as a man who did the decent thing and was sympathetic to M. Hayes until her coldness alienated even him.