I once grabbed a bottle of deck cleaner thinking it was windshield washer fluid (hey, same bottle type...), put it in my car, thought it was strange it was clear and thought it was just water until I looked at the bottle...
Well, it did work ok at first, but then it started drying on my windshield which resulted in the windshield wipers sticking and not cleaning the windshield correctly...it was raining that day too and I had to drive somewhere... I'm just brilliant aren't I?
I later got it out and now I will just use water, I think it works better than deck cleaner anyway...