How to refer to a theorem that you have shown to be wrong

I once saw a mathematician giving a talk about a theorem that he thought he had proved, for which a counterexample had later been found. He stated the "result" as follows:

Theorem (1983–1987): Let $A$ be $\dots$

(I made up the dates of birth and death)

In my opinion, it would be a bad idea to label statements known to be false as theorems. If you really want to do this, maybe you could put inverted commas around the word "theorem", to indicate you explicitly cast doubt on its following from axioms by applying rules of deduction. Or you could call it an Assertion, followed by a bold declaration that the assertion is false and the demonstration of such.

You can have a look to the paper "A counterexample to a 1961 “theorem” in homological algebra" by Neeman and use his style. By the way, I think that the paper is very very good.