The Casino Destroyer is a security guard who is suspected to be a terrorist and is plotting to cause an explosion at the Casino Floor in Las Venturas. The casino itself is small and located quite a distance from the gambling epicenter of the Strip. That could be a reason why the myth is not too popular.
This myth was started by myth hunter and YouTuber ulown00b. The proposition he puts foward is unlikely for two reasons: firstly, the suspected dynamite that the security guard is said to carry is not programmed to be carried by anyone in the game files, and simply vanishes when Carl Johnson acquires it. In the original video, ulown00b points out what he claims to be a ticking timer, however, this is most likely the gap in the security guard's hands and the door texture he is standing in front of - due to the low resolution and color filter applied, it could be misidentified as an object.This myth hunter also has a reputation for covering myths of questionable validity.
If the player goes to a dark corner, CJ will let out a deep breath, which could very well be a reference to the myth.