Clipping the O2 tube to your shirt stops the annoying twisting.
The poor man's O2 clip. See photo below. I cut 2 pieces of Velcro, wrapped the "hook" piece on the tube; "adhered" the "loop" piece to my shirt. As I'm not a seamstress, I just used the adhesive to hold it in place. A better approach would be sew it to some cloth with a button hole.
However, this approach could work nicely on T-shirts. Note use a larger loop piece if just using the adhesion approach, so it won't peel off easily.
ed
ps - Now if someone could solve the curling/trip hazard of these tubes my system would be perfect.