This is story related and cannot be missed.
Towards the end of the Bayou you will have to race Jimmy. This is afairly straightforward 3-lap race. Just make sure to avoid any logs in the water and look out for the speedboosts and you should have no problem whatsoever. These is also a very useful pipe shortcut in the second half of the track (can be clearly seen on the left hand side) which can save you a few seconds.