From an American sitcom Friends S08E13
Phoebe thought Joey liked her, so she went to Joey's to talk about this affair. But as the conversation went on, it turned out that it was Rachel that Joey liked, instead of Phoebe. After knowing that, Phoebe said, "Beat me over the head with it."
I don't understand the meaning of it. If she just wanted to express that message made her confused, just like using something beat her head, why did she use the preposition "over"? Specifically, for this sentence: "He beat me over the head with a stick", I would interpret it as "He brandished a stick over my head, just as menace, it didn't touch my head", so I feel "beat me on the head with it" is better to convey "I'm confused". Is there anything wrong?