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When a guy is having sex with a girl and he hits the back wall of her vagina.
My girlfriend is so small that every time we have sex, I hit reef.
by Nick77 April 12, 2008
When you're banging a chick and your dick is so long that it hits her cervix.
me: "dude! my new gf is so small i hit reef last night!"

friend: "bullshit, dude. you're asian."
by botokuno July 31, 2008