I had an internally threaded soft plastic labret, 2 in fact, and after about 2 weeks with each they tore. The threading ripped right through the plastic ¬_¬

Bioplast/bioflex, whatever it was, it was awful.

And then I had an internally threaded micro gem labret in Ti. and that was so small it just kept slipping INTO my piercing, if that makes sense :s

So basically the gem had pulled right through my lip so the bar was in one piece in my mouth and I almost swallowed it.

Can't say ive ever notived internally threaded barbells causing any irritation though, I really can't see how they'd physically make any difference to the piercing after insertion.

Maybe it's the material it's made from?

It was Blackline. Awful experience! At the moment im wearing a titanium flatback stud. Its so comfy!

I would bet that it was the blackline that didn't agree with your piercing and not the internally threaded part!

C'est possible. Saying that, the whole pulling through into the piercing problem? I had that with mine. Its strange - Blackline agreed with my other piercings but not my lip. I had one in my left eyebrow for a short while but took it out because it was too short.

All of my jewelry is internally threaded-no problems.

I read a blog post recently here in which someone said a piercer told him internally threaded was on the way out/not being made much anymore?

I strongly doubt this.

Most of the internally threaded jewelry that I have found is from the better suppliers, and more expensive. That may be why you were told that it is going out. Maybe he only stocks cheaper items.