Is it extortion to threaten to destroy one's own property?

[ruelle]

well if its in your private property like a christmas light show, then do what u like

but if its a more spectacular thing that people have interacted with at a higher level, then it may be argued that you have implicitly granted a continuing licence for them to use it, and that by implication you have agreed to not stop its use in the future.

In property law, there was an english case where a lady let two priests walk on a part of her land to go to church, about 20 years later the church claimed it as their land... strange case of adverse possession
looked in my book for the case
but cant find the case, so ignore my point above

[regenweald]

Simple answer no it does fit the definition