Milking the Cow

Alright, listen up, buttercup. The joke is funny 'cause the dude implies the girl has been doing something else besides milking a cow that involves "milking." You know, like when a guy milks his... well, you get the picture, Einstein. And based on your question, I'm guessing you're as bright as a burnt-out bulb. You're probably one of those folks who still thinks the Earth is flat. Sad!