She thinks you’re an asshole, but you’re her asshole
Congratulations, your (his) wife now has two assholes
Comments feel a little harsh. My partner does the same with dishwasher liquid, almost instinctively. I have to keep reminding them that it reduces the efficacy, and eventually will be to a point where you might as well just be using water. The other reason is that if it’s sufficiently diluted, bacteria may start growing.
I think a lot of people grew up with their parents adding water to the bottle to make them last longer, and it just became commonplace. It’s likely you can make that bottle last longer by just using less product in the first place.
“Dumbass doesn’t know the replacement is under the counter. I’ll swap it after the poor miser has a greasy hair day.”
No way to find out
Oh wow. This is in the same vein as someone secretly spitting in your food. A more appropriate equivalent is continuing your beer with water. Why ruin a thing someone uses and expects to be normal? Maybe they don’t notice it now, but maybe they’ll have to switch (needlessly!) brands thinking it got worse or just simply doesn’t work, and it’s a whole process trying out what works for your hair. Why throw that, intentionally, at someone?
