How this mod works:
Whenever CJ can hide the bulletproof vest under his clothes he will do it.
Moreover, the armour can only be seen when CJ has no shirt on, or when he is wearing the black or white tank tops.
Even the large tank tops will hide the armour.

Why would CJ do that?
It may not be so cool, but it's realistic:
-A criminal would hardly want unnecessary attention from peds and authorities.
-If his enemies don't know he's waring armour he's more likely to survive a murder attempt.
-Assuming that CJ wanted to intimidate peds in his gang territory you could still use another mod to remove his shirt when he arrives there and put it back on when he leaves.