A car runs over a man's head as he lies in the road. Only the characters in the car's reactions are shown (they don't see what happened and assume it's a speed bump), but the noise is quite graphic.

Multiple times various heads get into dangerous situations. Once a robotic head is displayed dismantled and later another robotic head gets squashed.

Not quite. There is decapitation, as well as one instance of a character's head slamming into a desk, resulting in a broken nose, but that's it.

Oberyn Martell's head is crushed by the Mountain.

Does a head getting eaten count as squashed? I'd say yeah, but some my disagree.

Twice throughout the movie a head is squashed, one being possibly the most gory death in the franchise.

In the first episode of Golden Wind Giorno uses one of his abilities to send the damage from an attack back to his attacker, Leaky Eye Luca. This causes the back of his head to cave in with an imprint of the shovel he was attacking Giorno with.

Yeah, a bunch of walkers get their heads squished throughout the show, there are so many instances of this happening that I can't think of just one example.

One gets ripped off, so yea

Heads explode in the game from direct gunfire and other assaults.

Two people die by falling, with obvious associated traumatic head injury, but no heads are squashed like by a car or other object smashing into it.

The main group runs over several corpses on a supply run. It's implied they run over a head but it cuts away and only a sound plays.

One character had his head bashed in by a metal ball, although I don't think there was any gore shown, only blood.

Two, technically. A person's head is repeatedly bashed into a porcelain sink fairly early in the film. This is EXTREMELY graphic and the aftermath is also shown graphically several times. In addition, another character's head is partially split with a cleaver, and while the action of this is offscreen, the character's ghost with the gashed head appears a few times.

In a very gory scene, a character is murdered by having a big stone spike from the church roof pushed onto him. His head and upper torso pretty much explode.

Beheading