As Barnaby examines the fire extinguisher the first time, the woman makes a comment about granny glasses. Jones makes a comment, then, about Granny not needing them. Both of these are references to Granny, on The Beverly Hillbillies (1962).
Actually it's not. While the reference to the Hillbillies makes sense, the joke here is aimed more directly to the then popular fashion accessory hippies often wore. Women especially wore "granny glasses", which unlike real glasses, were oversized, made of cheap plastic, and often tinted with psychedelic colors to emphasize their counter-culture use. People may not make the connection now, but old timers who remember those times do.
Actually it's not. While the reference to the Hillbillies makes sense, the joke here is aimed more directly to the then popular fashion accessory hippies often wore. Women especially wore "granny glasses", which unlike real glasses, were oversized, made of cheap plastic, and often tinted with psychedelic colors to emphasize their counter-culture use. People may not make the connection now, but old timers who remember those times do.