If you have a light colored carpet you could sprinkle small amounts of kool-aid powder into it that will activate when they go clean the carpets.
If you have a ceiling fan you could cover the top sides of the blades with glitter.
Whatever you decide to do, make sure you do it in a way where you are unlikely to get caught, or so that the consequences for you if you do get caught are minimal / nonexistent. If they end up getting the last laugh because they end up with a legal case to sick the cops on you (for vandalism or something), then it's all for naught.
If you can't add to their misery in a safe manner, you probably would be better off just settling for breaking the lease on them. Remember, landlords are typically little baby-fart motherfuckers when it comes to anything not going their way, so even just breaking the lease will bother them way more than you might expect.
In short, whatever you do, prioritize your own current and future well-being over compounding your attempt at revenge.
get some friends, move furniture through doors it probably shouldnt be able to fit through, make your landlord figure out how to get 3 couches and a bed out of the bathroom
I think there were some pretty lengthy posts in /tactics somewhere around the middle of last year about this topic.
