Yeah, probably a shirt. I've worn t-shirts backwards before and haven't even noticed. I feel like wearing pants backwards would be very uncomfortable, haha.
I would rather wear a shirt inside out than go wear a pants backwards. Imagine people seeing the pockets of my pants outside, their thoughts will be that I am running mad.
I'm the odd one out, I would rather wear my pants backwards since I own a few graphic tshirts and I want the artwork on the front of the shirt to be visible.