“Yytz they’re having a toeiva parade in Jerusalem right now. Yimach shemum v’zichrum, Amen!”
I’ve heard that we are not supposed to use this expression about fellow Jews no matter how low they have become. This is especially while they are still alive when we daven they still do Teshuva.
With the exception of Shabesai Zvi and Oso Ha’ish