first you have a member of jackass suit up in an old mans out fit. prefferably johnny knoxville. and in a busy area of town where there is a decent amount of steps. have the old man aproach the steps while reading a news paper or magazine and have him trip and fall down the stairs in a safe way but looks harmful to the people watching this horific accident. once at the bottom landing of the staircase groan in pain and agony as for you have broken your hip or some other part of the body. and then as quickly as it happened bolt from the scene so that you dont get arrested or have a medical team called to assist you.