Some time in the mid-to-late nineteen-seventies Lawn Darts became illegal in the USA. This, in my opinion, was the beginning of the end of Personal Responsibility in this country.
If a game that includes chucking a large, sharp projectile in the air and towards a TARGET that someone is standing near is not a case for natural selection of THAT ONE then I dont know what is!! For those of you who are too young to remember: DONT STAND NEXT TO THE TARGET!!!!

That being said, here is how you can replicate the fun of the previously outlawed game (of Lawn Darts, not Darwinian Blood-sport) with a few things that you probably have laying around the house. Keep in mind that you do this at your own risk/responsibility.

Heres what I used per dart:

1 20 oz soda bottle
1 - 6d common nail
1 3/8x1 bolt
2 3/8 washers
1 3/8 nut

Also:

1 220 volt MIG welder
1- 25,000 square foot scene shop with plywood floor (optional)

Step 1: Step One: Prep the Tip.

Weld 6d common nail to 3/8x1 bolt head-to-head so that the business end of each sticks out in opposite directions. If you dont have welding capabilities you could try using epoxy putty to join the two pieces. (If you try this then please let me know how it works out. My instinct says that it would work but will be tricky to make the bond strong enough.)

Step 2: Step Two: Prep the Cap and Bottle.

Drill a 3/8 hole in the center of the bottle cap (center is important if the washers are to fit later)
To lose the extra weight at the back, cut the bottom off of the bottle. I like the point just about a quarter inch below the label where the bottle starts to flare back out. Experiment. Find your best aerodynamic shape. (I'm sure you have the bottles to spare. How many sodas do you drink in a day?)

Step 3: Step Three: Assemble the Dart.

Put a washer on the 3/8 bolt, then the bottle cap (top first) next, another washer, then the nut. Tighten the sandwich with a pair of wrenches.
Screw the cap onto the bottle(s). At this point you should have an empty soda bottle thats missing its bottom and has a nail sticking out of its top. If the previous statement is true then you are ready to endanger small children whos irresponsible parents allowed them to wander into range of flying projectiles. (Really, I do believe that the thrower of the dart is responsible for its eventual landing place and the end result of having tossed it. [blame not the weapon but the wielder])

Step 4: Step Four: Targets!

I almost forgot.
These darts sink really well into 3/4 plywood. The aforementioned sceneshop floor is covered with the stuff. If you dont have such facilities available then you could cut out some disks of wood of any type (1/2 3/4 plywood is preferable. OSB works fine. 1/4 Luan is OK but the dart tip will probably go all the way through. A hoola hoop on the grass is great (Flashback to the original)) Mine are about three-and-a-half feet in diameter and set apart fourty-four feet. Yours should be the size that you feel is appropriate and set apart at whatever distance you feel that you and your dart throwing cohorts have a reasonable probability of hitting without unnecessarily endangering innocent bystanders.

Now it just comes down to throwing technique and rules. I prefer the two-fingers-inside, underhand, palm up method though I have co-workers who swear by the thumb-inside underhand, palm down technique. All pretty much agree that an overhand throwing motion is only useful when going for the distance record (currently- 1 point from 86 feet)
As far as the rules go, we play with a three-ringed target. The rings are valued at 1, 3, and 5 points (bullseye=5, white ring =3, blue ring=1). Games are usually to 11 points. Any dart that lands on the line between two score values counts as the lower score(we're harsh that way.) After a round of shooting at one target the player who scored best in that round gets to throw first at the other target. (Honors for the golfers out there.) This gives the best thrower the slightly unfair advantage of a clean target. You could reverse this rule but I doubt it would make much of a difference. The "must win by two points" rule can add a level of challenge as well.

Either way you go, Good Luck. Throw Straight. Have fun! Claim your dart when it lands! (Wherever it lands!)