I see two things you did that that would antagonize almost any captain, including you someday: 1) you apparently just spun back his speed without maybe suggesting he may want to slow down first. Excuse me?! Better CRM would have been to suggest that "maybe we should slow down because it's pretty bumpy". Give the guy a chance to make the move on his own. Hell, I'm a captain of MY airplane, and that's the type of suggestion I would make of a first officer during his/her leg. It's just damn rude to spin it down when it's not your leg.
2) Concerning the red cell, did you first suggest that maybe you should ask for a left or right heading away from the cell? If so, did he just ignore you, or offer up a reason why he was planning to penetrate the cell?

CRM goes both ways. You know that. Work as a TEAM. Your actions, at least the way you've described them, strike me as the actions of someone who feels he knows it all, and has to act as the real captain onboard your jet.