I Hope this cheat code works. If not, I dunno.
At the main menu, Enter the following cheat codes.
If the cheat codes not work, try them out during gameplay (If They Work) Or try them elsewhere. If This Fails, I'll look for a solution myself. I will be testing them out this week at the most.
At the Main Menu, Press L2, L2, Circle, Circle, Square, Circle, Triangle, Circle, L1, Circle, L2, Circle.
All Jackass Characters
At The Main Menu, (See Above) Press L1, Circle, Left, Left, Circle, L2, L2, Right.
Unlock Bam Margera
At The Main Menu, Hold L1 and R1 to do the cheat code sucessfuly. It's Circle, Square, and X.