Be the bigger man and just walk away.
I was in this exact same situation once and considred doing all manner of things (roaches through the mailslot, mice through the mailslot, some sort of noxious gas under the door) but in the end I wrote a very strongly worded letter and sent 1 copy to the tenant, 1 to the apartment maanager, and 1 to the property management company and took solace in the fact I was moving on to biggger and better things, while they were all stuck in the same place.
I know nobody probably cared about the letter, but it made me feel better, without having to lower myself to their level of immaturity.
KT
I was in this exact same situation once and considred doing all manner of things (roaches through the mailslot, mice through the mailslot, some sort of noxious gas under the door) but in the end I wrote a very strongly worded letter and sent 1 copy to the tenant, 1 to the apartment maanager, and 1 to the property management company and took solace in the fact I was moving on to biggger and better things, while they were all stuck in the same place.
I know nobody probably cared about the letter, but it made me feel better, without having to lower myself to their level of immaturity.
KT