A lighter isn't a good concussive device because it's flash point is rather high, exhaust gasses that far back might not even light the fluid. It will pop, but it will most likely just be the pressure escaping as the plastic melts. Things that explode do so the best when an internal force overcomes the container's structural integrity. Blowing up a ligher is done by weakening the integrity of the container, thus allowing relatively low pressure gas to escape. We used to throw boxes of disposable lighters into the fires that bums would make out of barrels under bridges. The fire would melt the plastic, the fluid would rush out and ingite. Big fireball, but no concussive damage.
Depending on where you live and what the traffic enforcement devices are like, you should steal his license plate for a night and run all of the red lights that have cameras. Then he gets multiple tickets sent to his house. He won't have to pay for them because when they review the photos, it won't be his car, but he'll still have to deal with going down to the courthouse to take care of it. Do it in a cheap rental car so there won't be photos of your car doing it.
Or if you know he's going to be out of town for a day or more, put his plate on a car and park in no parking spaces all day long.
Or if he has hubcaps, stash a bunch of fish fillets behind the cap. In a few days his car will reek, and gods help the next person who takes that cap off.
If you're mechanically inclined and have access to his unlocked car, wire the horn up to one of the turn signal lights. Every time he makes a left turn, beep beep beep beep. Drive him bonkers.
If his gas cap doesn't lock, buy one of the cheap locking caps at AutoZone. Install. Enjoy.
Take a screwdriver, remove his rear plate light (or if you want to be a real jackass, cut the wiring harness going to said light). He probably won't notice that it's out until he gets pulled over for it. Extra points if he has a warrant and goes to jail. You just made the streets safer.
Most cars made in the last 15 years or more have a fuel cut-off switch that is activated by a hard impact (so if the car is in a wreck, fuel doesn't get pumped all over the place. Research the type of car that he has and where this switch is. In most of the cars that I owned with this switch, a solid thwack with the heel of my hand right in the area of this switch was enough to activate it without causing any external damage. He gets in, car won't start, and trust me, it's that last thing anyone would ever think to look for if their car won't start. Be ready to sprint out of there in case he has an impact sensing alarm, as it will likely go off as well. Works best of you know someone with the same type of car as the target so you can find out if it works properly, as certain cars might not be as vulnerable to this.
Hang (on his side mirror or door handle) a bag of Turtle Wax products with a card saying something about "Free Promotional Gift Pack" Everybody likes free stuff, right? Problem is, unbeknowst to him, you mixed two tablespoons of gritty sand into his Liquid Wax formula (two tablespoons is enough to get the effect without thickening the mixture suspiciously). He pours on wax, rubs vigorously, and viola!, swirl mark and scratch city.
Wrap toilet paper around his exhaust manifolds and leading pipes (the parts furthest forward, closest to the engine, in case you're not familiar with auto terminology). After a minute of driving or so, those will flash and produce copious amount of smoke from under the hood (however, there is a chance that an older, greasy engine will continue to burn after the TP is all gone, so I don't really recommend this, he could lose the whole car or possibly be injured).
Many older cars (60-70s) have the front seats attached by nuts which are accessible from under the car. Remove the front two, and when he accelerates, the seat will flex back, creating quite an "oh sh!t" moment for him (somewhat dangerous, if the rear seat bolts were to break as he was accelerating onto the highway or something, and he ends up in the back seat while traveling 60MPH, also not recommended due to the danger to others).
If accessible, pull all of his spark plug wires, or switch their locations on the distributor cap. Car no starty starty, call mechanic. Pay towing charges and at least an hour labor to a shop to get it going again (unless he his mechanically inclined).
I have dozens more, but I'm sure my liability is high enough already without getting into the really dangerous ones....
