Well, I'm (much to my surprise) the VP of Opperations for a currently very small (and very new) DSL ISP.
One would think that I'd have to wear a suit. But lucky for me, even the CEO wears just a polo shirt and slacks. The CTO usually wears jeans and a polo shirt. I usualy wear slacks and a nice shirt with a collar.
However, the ISP shares a building (which is mostly one large room) with another business owned by our parrent company. That other business is a telemarketing firm. Enough ink in the tattoos write a novel and enough metal in the piercings to make a small car (okay, not really, but you get the idea). To get to the point, I could probably get away with a t-shirt and shorts. =)