First of all make sure you are in goofy stance (facing left) then throw the board with RT and turn 90 degres right.

Then in this exact order and not too fast press A, LT, RT, Y and up on the left joystick.
I don't know if this is patched but if it it is you can do it another way.

Block off a road, and wait until a sports car with big spoilers comes.

Jump on it, then go right to the back of it. Make sure your foot is hanging over the edge of the car.

Also make sure your foot is not on the spoiler but inbetween the roof and the spoiler.

Then do the same combo as the other glitch.