Slowly enter one of the following codes before a match, while your character is speaking to the opponent.

1 - Up, L, Down, Y.
2 - Left, L, R, Right.
3 - Down, X, Up, R.
4 - L, R, Up, Down,Y, X, Left, Right.
5 - Up, L, Up, R, Up, Y, Up, X.
6 - Left, R, Up, X, Right, Y, Down, L.