It is an old-fashioned term made popular by the Earth First! folk in the 70s. It means stopping something industrial or mechanical from working, wrecking it as much as possible relative to the difficulty and time it takes to achieve. Think putting something in a gas tank… Or undoing some critical bolts.
Expanding Foam – by definition it is intended to gunk up a space when the access might be limited, like a hole in the wall. Give it a go with any equipment that had a hole. Fill up a letterbox, stop an (old-fashioned) alarm bell from clattering.
Super Glue – just like expanding foam, this can be reversed (with effort), but repeated annoyances can sent a powerful message. Glue might be good for a vending machine flap where the product comes out. It will take them a day at least to notice and fix it.
Calcium Carbide – is a solid that reacts violently when it comes in contact with water. The resulting acetylene is flammable (and explosive if contained) and smells horrible. It is also dangerous to your health and you need proper protection and storage when using it. And research carefully, this stuff is powerful!
But yeah, one idea is you drop in into a toilet being flushed and it will wreck the plumbing. That’s a lot of bang for buck.
Pyridium makes someone’s urine orange (or more orange) and Methylene Blue is a harmless chemical that makes urine blue. Add these to someone’s food or drink. Similarly but more nasty, Ipecac and Antibuse will make someone throw up, the latter requiring them to drink alcohol. Great party trick! Or, you know, corporate events…
Sodium Silicate Liquid – is sometimes called Water Glass. This is what it does to an engine 33 seconds down the road:
Also, a Pocket EMP might be able to brick some electronics. You’ll need DIY skills. And somehow cart a large battery around (or wait for battery tech to improve)