GAW,
My understanding is that schok is assur because it is a type of activity that is margilin l’erva. It is a gezeira that applies to people even if they are certain that it won’t be margil them. (?????? ???????? ??????, ??????? ????????? ?????, ???????????? ????????? (Avos 3:13)). If a gezeira only applies to the action when it is undertaken with the intent of being margil l’erva, then just say it is assur to be margil l’erva. Remember chibuk v’nishuk with ishto niddah is assur even without any intent.
The Shach is explaining kalus rosh with words. He is saying that if these are the types of words that are margilin l’erva, it is assur, regardless of any actual intent to be margil. I think you’re better argument is that this type of fun is objectively not schok. But that begs the question of what activities would constitute schok.
With respect to married couples, because they are already married the are not trying to laugh and have fun together to strengthen (or create) their non-platonic relationship, they are just going about their regular day. But to go out on a date-night to an arcade b’es niddasa would be assur.