Put glue around three edges of a piece of tissue paper then stick another piece (the same size as the first) to it. This will make a pouch with one open side.
Fill the pouch with glitter and glue the fourth side shut
Now put glue on both inside pages of a Christmas card, and stick your glitter pouch to it. Now pop your card in its envelope and give it to someone.
When the card is opened, the tissue paper will tear and glitter will snow all over your victim - gotcha!