PAIN

This can be done in Fail Village and it's very easy. Granny is the snowboarder on the halfpipe. Grab a throw present (red box with the green bow) from the tower to the right of the halfpipe entrance and ooch up into the halfpipe. Hold onto the present and spin the camera around so you can see Granny. Wait until she comes near you, then let go of the present to let her have it. As long as she is knocked off her snowboard by the explosion, you'll get the trophy.