Joy Ride 2: Dead Ahead

The film begins with a trucker at a truck stop in an unspecified rural location. It is night time and in a heavy rainstorm, and a hooker gets into a large, black Peterbilt and offers her "services" to the trucker inside. The trucker is revealed to be Rusty Nail (Mark Gibbon), when he recites his phrase "I like the rain. Keeps everybody inside and washes everything clean". He asks the hooker to go out into the rain to get wet. When she is unnerved by this strange behavior and states she is leaving, Rusty Nail locks the doors and asks her to leave through the open window. He then shuts the window up half way as she is clambering out, trapping her with half her body hanging outside the truck. Rusty Nail then drives off, decapitating the hooker as he drives alongside a trailer attached to the truck.Meanwhile, Melissa and her fiancé Bobby (Nicki Aycox and Nick Zano), a young engaged couple in their early twenties who are on a cross country road trip in a 1983 model Chevrolet Caprice Wagon. They are heading across the Southwestern United States to Las Vegas, where they plan on getting married. Joining them for the ride is Melissa's sister Kayla (Laura Jordan), who along the way also picks up her online boyfriend Nik (Kyle Schmid), a punk.When their car breaks down in the desert, the four find a seemingly abandoned house along a side road and in the barn they find a silver 1971 Chevrolet Chevelle with gasoline fully filled. At first Melissa and Bobby are reluctant to take the car as it amounts to thieving but due to Kayla and Nik's persistence they relent. Melissa, Bobby, Kayla and Nik decide to take the Chevelle as there doesn't seem to be anybody about and the car is in working order, however Melissa leaves a note in the house leaving her contact details to whoever may own the house and/or car.Melissa receives a phone call from the person who owned the car they stole. He then calls Melissa Goldilocks (she is blonde), revealing that he can see her. It appears somebody had followed them, and he also tells "I believe you have something of mine, cause I have now something of yours." as soon after Bobby disappears from a diner restroom. The others find a CB radio in their car with which Rusty Nail talks to them. He orders them to destroy their cellphones and follow his orders if Bobby is to survive, and he has some quite nasty psychological mind games that create a bridge for gory, life-and-death situations. The group continues to follow Rusty Nail who promises them that they will be all reunited soon, after Rusty requests for Kayla's middle finger, a reference to when Kayla flipped off the driver of a truck. (Rusty's) The group cut a finger from a corpse and they reach a wrong trucker because Rusty already knew that they had broken the rules. Rusty cut off one finger of Bobby and put it in the glove compartment of the vehicle which was later discovered by the group.Rusty later instructs Melissa to "strip down to her underwear" in front of his truck, but it turns out not to be him, but some other trucker Rusty Nail had instructed to be there. Rusty Nail soon pulls up at a bar in Utah and Bobby tries to escape. He gains the attention of the barman who has gone outside to smoke, but Rusty Nail catches him and uses a chainsaw-chain to cut off the barman's jaw. He then commands Nik to walk through a party dressed as a female and to buy crystal meth. Nik refuses to do this, and Melissa takes a knife to his throat and Nik cries, confessing he is scared and that his tattoos are fake. Nik walks up to the party in the clothes that were seen on the hooker earlier, but at the party Rusty kidnaps Nik and drives off. Melissa and Kayla chase them, and Rusty gets behind them. He rams them a few times and then the car flips over, and Kayla's leg is pinned and instructs Melissa to go because he's going to ram the car again. Melissa jumps at the last second as instructed, while Kayla is killed in the exploding car.He takes Bobby and Nik back to his home, and has them play a sadistic game with dice. In this game, whatever one person rolls makes the other person suffer. Various things happen to them, like branding them with a rusty nail in the shape of an "R", being hit in the kneecap, etc. Once Bobby rolls a double one snake eyes, Rusty kills Nik by stabbing him with a steel bar through the top of his head. Melissa then breaks into a police station and steals a motor bike and races off to find Bobby. Rusty nail hangs Bobby by his neck in the back of his truck. Melissa comes to rescue him by distracting Rusty Nail with the police motorcycle, by parking it by the side of the truck. Melissa overpowers the killer with a few well placed hits to the back with a shovel and drives away in his truck accidentally disconnecting the cab from the rest of the truck (leaving Bobby behind), only for Rusty to manage to grab on to the side and end up on the roof of the vehicle. She drives until the sun comes up and ends up plowing into a gas tank, causing the truck to catch fire. Melissa jumps from the truck as Rusty takes control, but it's too late and he drives off the side of a cliff, the truck exploding on impact.Bobby escapes from the trailer he was hung up in and meets back up with Melissa, their ordeal finally over. Later in the middle of nowhere, a girl is stuck on the side of the road as her car has broken down. A big red Peterbilt truck (with trailer) drives past her, only to back up. She explains what's happened and asks for a ride. As the truck door opens you can see that the driver has a badly burnt right arm. The girl climbs in and a familiar voice says: "You'll catch your death out there", before laughing ominously as the credits roll.

Question: How does Rusty kill Nik