Do the following in single player mode:

-pic Blackjack mode
-pic any room
-pic the third table (the blue with the blond girl)
-pic any cue
-pic any ball set (I usually get any but the first set)
-pic Walker (the guy with the cap)
-pic any song
-pic Medium ball speed
-start!

You just have to charge the cue fully without moving it, just hit straight... Ball 14, which is in the bottom right of the triangle, enters.

One more time, charge the cue fully and hit straight, don't move it!... in a weird chain reaction, the 7th balls goes right down where 14th ball just entered.

You got 21, you won.. and get the goodies.