go out and buy a 9MM, hide it under your pillow, and during sex pull that fucker out and put it to her forehead and scream "IF YOU DON'T CUM 5 TIMES BEFORE ME, YOU WILL GET CAPPED!!" then proceed to pound the fuck out of her... she will be scared at first, but when the cumming commences she will go bananas and love you afterwords... atleast thats how it worked with me and my sister
