Simply Sunday. I am honestly appalled at how friends of mine travel. They seem to think that travel is an excuse for dumbing down and then they wonder why they are not treated with respect.
In London, The Ritz has a policy of no jeans, no sneakers, regardless who you are. In public places in that luxury hotel, you are simply not allowed in. The knowledgeable know this, and do not try to look like bits of garbage.
But throughout the entire travel process, including planes, trains and buses, and ships, you are honestly treated better if you dress well. Keep scruffy, smelly, obnoxious for your home, if you must. But treat those who are serving you with respect and, know what, YOU will feel better if you are dressed suitably.