Just commit, no matter the response. Adding /s is akin to explaining a joke after you tell it. If someone doesn’t understand or pick up on the sarcasm, it’s not your responsibility to spell it out for them. You add /s because you don’t want to be held accountable.
Not even idiots. Sarcasm is entirely culture-specific. Even two native speakers from different cultures can easily mistake a sarcastic text for a serious one, and vice-versa. This doesn’t even touch the difficulties ESLLs experience with online sarcasm.
But I still don’t use /s because I’m a lazy fuck.