[Kirk just needs to give it time--time here, preferably, where he's more of a friend than a leader. Chekov still adheres a little too rigidly to roles and titles; anyone he's mentioned Kirk to here probably thinks that his first name is "Captain."]
Don't go easy, please. I'm stronger than you may think. [He did haul Kirk's (and Scotty's!) ass over a railing that one time.]