If Shmeryl made an active decision to throw Judaism out the window, the Chofetz Chaim says that the prohibition of lashon hara would no longer apply to him.
Otherwise, given today's usual circumstances and usual listeners, to say "Shmeryl wasn't raised keeping Shabbat and doesn't (yet) observe it" will neither upset Shmeryl nor harm him (unless he's trying to keep this a secret or something).
Need to get the source on this, but from what I recall reading in Chafetz Chaim, I believe a good definition of lashon hara is:
A.) Telling something about Mr X if Mr X would be upset if it was said in his presence. OR:
B.) Telling something about Mr X that would prove harmful to him.
It's done specifically as-needed for a productive purpose.
But there are situations where one may fib to avoid lashon hara; e.g. "did Shmeryl say anything bad about me?"
(Need to provide citations from Sefer Chafetz Chaim about all this.)