The top five ways to torture a Mary Sue.
1) Tell the Mary Sue no one likes her. At all.
2) Start a prank war against her and really mess everything up for her.
3) Send her a present that turns out to be something unpleasant.
4) Tell her someone is in love with her - then give her the directions to Mordor.
5) Do number 4 but give her the directions to Isengard.