I knew a guy that planted horseradish in his backyard garden, and within a couple of years it had taken over his entire backyard, with these big, ugly stalks.

He had plenty of great, sinus-clearing, eye-watering horseradish, though.

Since then, I've always thought that surreptitiously sticking a stick of horseradish in an enemy's yard would be an excellent revenge strategy. By the time they realize there is a problem, it will already be way too late.