I haven't heard "hay is for horses" since I was a child many years ago. The other day, I saw my wife in the kitchen and called out "Hey, could you bring me a soda?". She stood in the doorway and yelled back "Hay is for horses!". I don't believe she'd ever said that to me before in over 30 years of marriage. I thought I was the only one who ever heard that expression growing up.