Hold 'select' button (on PS3, unsure of corresponding button for 360) to bring up the menu where you can set waypoints and access inventory etc. There is an option in there to remove the bulletproof vest. It may be under 'inventory' if you cant see it right away. Cant get to my console at the moment to give the exact option name. You will still have the benefits of the armor, but it wont be visible.
- MhastaChainx likes this