Dress code for short haul upgrades is one thing but I think on long and medium hauls it is more likely to make you stand out as nonrev, simply because most if not all the paying punters are travelling in their casual clothes. There's nothing wrong with a neat pair of jeans, presentable shirt and a clean pair of trainers. It's time airlines became a little more realistic with dress code vis-a-vis upgrading and staff travel. I'd still say no to torn jeans, shorts and loud t-shirts etc.