"Thou Goatish, Fly-bitten lout!"
"Thou dissembling, hell-hated lewdster!"
"Thou villainous earth-vexing maggot-pie!"
Of course if you're aren't feeling particularly vicious and you'd rather say something nice, you could always woo someone with Shakespeare's famous lines of love:
"The course of true love never did run smooth."
"I love you more than worlds can wield the matter, Dearer than eyesight, space and liberty."
"Doubt that the stars are fire, Doubt that the sun doth move his aides, Doubt truth to be a liar, But never doubt I love."
And that, my dears is just a taste of why the man is THE Shakespeare.