Well thanks for setting me straight. Dunno why military fighter pilots don't practice this maneuver more.
Because they have way more sense
Not to mention that pilots with blood shot eyes don't look cool, so they don't have much luck with the ladies
Now the serious response for anyone reading this who might think negative g is a good idea.
Human tolerance to negative g is much less than positive g so any maneuver you try under negative g will be very much less effective than its positive g counterpart. So much so that nobody ever spends much time experimenting with negative g maneuvers before realizing there is no advantage to be gained from it. I can't imagine any situation in combat when attempting to execute a barrel roll under negative g would be advantageous.
The simple fact is that anything you do with positive g will be more effective.
Situations where negative g might be appropriate include a simple push over, which has numerous applications, a negative g guns defensive and the early stages of a spin recovery.
I suggest that anyone who thinks negative g maneuvers can be used to win fights, needs to spend some time with a trainer, the misconception will be short lived.
Regards
Badboy