Ugh, my posture is shocking, and I know it. The scholiosis doesn't help at all, but for the most part it's laziness and insecurity - I'm always unconsciously trying to shrink myself down and hide from people (IRL of course lol, nobody online can see how hideous I am hehehe). I do try to maintain better posture when I think of it, but I admit it's not often the thought occurs to me that I'm slouching.
*shoulders back* Thanks for the reminder, Rouge! Good resolution, I hope you can keep it up!