You can use Baby Spice - Item - World of Warcraft on a tank and it makes it very tiny while you remain big. Pretty funny. Alot of times the enemy doesn't notice and it gives me enough time to break a wall. Also if you use bloodlust or elixir of giant growth you can become really out of proportion.
Probably works with wg vehichles aswell. Not sure if it affects the hitbox tho.
http://img27.imageshack.us/img27/7030/wowa.png
Edit: You get the item from doing the cooking daily. Its a fairly good droprate.%26lt;
by wootpeng