Wedding attire

When did it become acceptable to wear jeans and polo shirts to a formal wedding?
My girlfriend and I were visiting this evening about wedding attire. We have seen it all, trust us! A wedding at the Plex yielded up short, short skirts, gladiator stilettos, jeans, polo shirts and dockers! To a wedding? Whatever happened to respect for the wedding couple, the event and yourself?
When did receiving a wedding invitation mean that it is just another event; no reason to make it special, I don't-need-to-go-out and buy a new outfit? Clean off the stains from the golf shirt, hitch up your jeans, and don't forget the baseball cap, because we are invited to a wedding!

Come on folks! Have a little respect for yourself if not for the occasion!