...To clarify my question, imagine you are in a glory hole booth and you stick your dick thru the hole and someone on the other side (the adjacent booth) has the flu and sucks your dick BB.
Can the flu be transmitted this way?
To be successful, viruses typically evolve in such a way that they can easily infect their host, replicate abundantly and shed themselves so that they spread readily and infect other hosts. The influenza virus has evolved to do this very successfully by exploiting respiratory tissue in humans. The virus, over countless generations of evolving and mutating its genome, has developed a preference for specific cellular receptors found in greatest concentration in the lungs and airways on which to fasten their viral attachment proteins. Different flu strains have evolved to attach to different cellular proteins and so some strains (i.e. H5N1) attack tissue deep in the lungs causing more severe infections than those that attach to upper respiratory receptors.
These receptors are not found in significant concentration in urethral or vaginal mucosa so, for the same reason your stomach is generally not bothered and you don’t get skin rashes when you contract influenza, your urogenital system is unlikely to be affected either. Remember though that the viral load in the saliva of a flu sufferer is high and any contact with it (pulling your dick out of her mouth and back into your pants, then touching your hand to your face) would likely inoculate you by the respiratory route (nose or mouth). But no, the bug won’t travel through your dick up into your lungs.
Evretou is right, your best defense is a flu shot, but even that is only as good as the best guesses of the epidemiologists and in some years the vaccines may be virtually useless in preventing the disease.