This saying was said by my informant’s father to her whenever she stood in front of the television. He would say “you didn’t drink your Windex this morning”, and my informant now says this whenever she finds herself in a similar situation.
Windex is a window and mirror cleaner, and so presumably this saying means that you are not clear enough to see through (and you would be if you had ingested Windex). It could only have come into existence after 1933, when Windex was first produced. It also indicates the commonality of the product and the issue, as there is a saying incorporating a brand name product in a situation that became more and more prevalent as televisions began to enter homes.