It can be insulting to your coworkers or clients to show a lack of concern about your appearance.

Being wrinkled, unshaven, smelly or unkempt communicates (intentionally or not) that you don’t care enough about the situation, the people or the company to present yourself respectably.

If in doubt, always err on the side of conservative. If you think jeans may be OK for a social event but aren’t sure, show up in ironed khakis and a nice golf shirt. If you think a situation may call for dress slacks, wear a dress shirt and tie. If you have any inkling that a suit may be called for, dress to the nines.

Women’s clothing is a bit more complicated, but again, err on the side of conservative and dressy.

Always practice impeccable grooming (even in a jeans environment!)

(Business Etiquette refference)