I am a strong believer dressing, saying and doing exactly as you please, but dress codes do have some value. Dress codes are designed to make everyone feel more comfortable, they are an official social equalizer.
Under-dressing despite a written dress code is one of the most common and least sensible breaches of etiquette. It says a lot.
First and foremost, under-dressing expresses disrespect for the host and venue. Wearing cocktail to a formal event openly says ‘your event is not worth my effort’. Yet people, good, kind, polite people, do it all the time, there must be a strong motivator behind this phenomenon.
The motivator is insecurity. Disrespect for one’s peers is a classic sign of personal insecurity, because it’s a fairly effective method of dealing with said insecurity. When a person puts their peers down, they feel elevated above those peers, which makes them feel more secure about their social status. Most people do this periodically, when threatened. I certainly do, even though it makes me look like a twat. Most people find an event with a dress code mildly intimidating, and the natural response for many is to employ an easy, undemanding form of disrespect toward the threatening party (the host or hosts).
There is also an element of fear that accompanies formal attire. Being ‘dressed up’ attracts attention, which is, in itself, undesirable to some. Attracting attention comes with its own set of personal threats. What if you look silly, or fat, or over-dressed? If you’re over-dressed, will everyone think this little party is the most exciting event of your year? Under-dressing is beginning to look like the safest option, but don’t let anxiety control your decisions. Under-dressing makes people look both disrespectful and insecure, and neither of those traits will do anything flattering for anyone.
Under-dressing can also imply many things to fellow guests: poor education (not understanding the dress code), poverty (inability to afford anything that could fit the dress code), social inexperience (never being invited to such an event before), and even gate crashing (not receiving an invitation and therefore not seeing the dress code).
Over-dressing is rarely a problem to anyone. Hosts feel validated by it, venues like the apparent social elevation, guests feel more confident about their own formalwear, the wearer is complimented all night and their date feels lucky and proud. Of course, dull, jealous under-dressed women sit in the corner sniggering, but given the choice between joining them, and being their newest idol, I know which I would choose. It is a problem when you outshine the bride/birthday girl, wear something uncomfortable or look truly out of place, but I think you can avoid such problems fairly easily.
I trust you to dress up, trust yourself.
Yours, very truly indeed,
P.S. What do the various dress codes actually mean? That is an article for another time, but until then, Wikipedia!