User blog comment:DazzlingEmerald/The Hyuga/Ōtsutsuki Bandwagons Are Coming..!/@comment-6003865-20141031232952/@comment-4961229-20141101185535

"someone cussing like he knows it all" LMAO! Now ain't that the sink getting scolded by the commode over germs, mildew, and mold. Ass is a very mild and common word, stop pretending as if I cussed you out. I've seen you use a few four letter words youself.

My knowledge of the manga is apparently much better than yours. So is my logic. "Garbage in garbage out." You've forgotten the necessity of inputting actual manga facts into your mental gyrations in order to come out with something approaching useful. This you have not done.

If the Byakugan had such a weakness as you describe it would not have been coveted by anybody, not even the people born with it. Hyuuga's would be the most vulnerable of all ninjas. An Uchiha could look at the backs of their skulls and genjutsu them. An enemy could cast genjutsu over an area as we've seen in times of war and if anybody with a byakugan happened to look into that area they'd instantly fall into genjutsu. They'd be extreme liabilities in any conflict against anyone with strong genjutsu. Somehow though neither Obito, nor Madara ever thought to genjutsu whoever that Hyuuga was who kept, 1) Yamanakaning his ass and 2) Blocking his juubi toothpicks when he was trying to murder Naruto.

Thus a hyuuga would be the absolute last person that you'd want to ask about whether or not you're in a genjutsu as they'd already be inside whatever genjutsu was aimed at you. Instead you'd just look at them flopping around on the floor, like a miner's canary, and say, damn, looks like genjutsu's afoot.

Nothing like this nonsense has ever even been hinted so it is most likely your fan fiction head cannon.