https://imgur.com/a/fDwMw (link mirror to image)
Alright, this is a tutorial of sorts, but a word of caution: This is kind of dangerous to do so wear gloves and maybe have a fire extinguishing method nearby.
If you have spare sections of PVC, whether it be short lengths of 3 inches or even a foot long, you can make effective and cheap road sabotage tools known as "Caltrops". This method I came up with but it probably has been done before.
Wipe down your PVC sections to remove fingerprints and work with gloves for the rest of this process, preferably cloth to insulate from cuts and heat as well.
Take your PVC sections and cut lengthwise halfway down the section, then rotate ~90 degrees and do the process on the other side. Take two pairs of pliers or wrenches and heat the PVC over a heat gun or stove top. Make sure not to burn the PVC and evenly heat the section until it becomes malleable. Warp the sides of the PVC using the pliers so they jut out at sharp angles. The idea here is however you throw the "caltrop", it will always land with some sort of sharp edge pointing up and out. Hold the shape until the PVC cools down enough to retain the shape. Repeat the process for the four other sides.