Silly question. Jeans and t-shirt. On a more interesting note, some old-timer (I think Jerry Weinberg) said that the reason hi-tech dress codes are so lax is that in the early days of computing, programmers were so scarce that they could get away with pretty much whatever they wanted. With the notable exception of IBM ("go home and don't come back until you're properly attired"), many companies were unable to enforce what they considered correct behavior. I for one am very grateful to our deviant forebears.