An air carrier First Officer described the actions of a Captain who refused to comply with ATC's speed requests. The Captain denied both ATC and the First Officer's admonition that compliance with the speed requests were reasonable.

Narrative

I made this Captain aware of that fact when I noticed that he was deviating from standard speeds in climb; cruise and descent. I tried to make allowances such as informing ATC that we would be cruising at .73 even though we were filed at .775. On the flight in question; we were on the arrival and were assigned 250 KTS for spacing. We were then assigned 300 KTS. The Captain reluctantly accelerated (slowly) to 300. We hit a little bump (no more than a moment of light chop). The Captain said 'turbulent penetration speed' and slowed to 280 KTS. I informed ATC that we were slowing for the ride. ATC asked us to resume 300 when able. A couple of minutes later ATC asked us to resume 300 KTS. The Captain said to tell him 'NO'; we were going to maintain turbulent penetration speed. It was smooth. I looked over to him as if he was kidding. Whatever I looked like; it set him off. He said something to the effect that he was the Captain and he was going to fly the plane the way he saw fit. He said he would talk to ATC. He proceeded to tell ATC that he was telling them that he told his First Officer that in his determination he felt he need to fly 280 KTS for the safety of the flight. ATC said that everybody else was doing 300 and nobody had complained about the ride. We were then told to maintain 280 KTS until further advised. ATC later asked approximately six other flights (all same airlines) to say ride conditions. Each and every one of them said 'smooth.' I don't want to go down for this Captain's greed. It will catch up to him in the end. I understood with ATC wanted and why they wanted it. I didn't see any reason why we could not have complied. We have about 30 seconds of light chop but the didn't warrant 280 KTS all the way to approach's sector. I tried to use CRM but it seemed ineffective with this guy.