The cabin itself is a social situation in which I felt obligated not to cause a scene by starting to question the flight crews over something that must absolutely be administered. So I just accepted the spray and I count myself lucky that it doesn't have any adverse effects on me.

I did want to say something, and there's a very small chance of misfortune, in which i probably thought "it won't happen to me".. but it remains as something that could be improved (as in procedure of informing) , and yes agreed i'm at wrong there as i let it slide.