-You should dress to impress. An expensive-looking outfit will get you better treatment....even if its from H&M. Remember that Friday and Saturday nights can be more difficult to get into a club, and being impeccably-dressed gives you an advantage.
-The standard Vegas look is a collared, button-up shirt and tie worn with jeans or dress pants and leather shoes. It's not too original, but is guaranteed to get you in the club.
If you insist on wearing a t-shirt/Vneck, it better look like something special.
A simple way to dress up a t-shirt is to wear a sports coat over it, but youll see everything from Vegas "Guidos" wearing the typical ED Hardy to the Hipster/preppy/nerdy/HB/Ne-Yo lookin ass.
-Some up-scale clubs forbid jeans and t-shirts. If you're concerned, check their website or call in advance to find out what their dress code is.
-A suit is fine, but unless you're 007 you might feel over-dressed...but not likely.
-Please don't try going to a club wearing a tank top no matter how buff you are. It's not likely to work out for you....
-Even if the club allows jeans, you shouldn't push your luck by wearing ones that are really baggy or torn. If you have no other choice, make sure you have some "fashionable name-brand" shit or keep it real dark. Keep in mind that Vegas is like Hollywood.
-No baseball caps, jerseys, or shorts. Ever.
-Forbidden footwear for clubs are sneakers/dunks/kicks/airmax90s/timbs, sports sandals, and flip-flops.
-Don't assume all clubs have the same dress code. Just because one club allowed you in wearing a t-shirt doesn't mean that the next one will, and arguing won't help.