Enter at the main menu.
One hit knock outs --> Hold L1 + R1 and press X, Circle, Circle, X at the main menu.
Chicken-head people --> Hold L1 + R1, press X, O, O, Square
Disables all heads-up displays (HUD) --> Hold L1 + R1, press X, Square, Triangle, O
High speed --> Hold L1 + R1, press O, O, Triangle, Triangle
Japanese Crash skin --> Hold L1 + R1, press Square, O, Square, O
Run into a car for an automatic KO --> Hold L1 + R1, press X, O, O, X