Spock shows emotion on Star Trek all the time. He's playfully irritated with McCoy, he's loyal to Kirk, caring of the ship and crew, and very easily embarrased of his human side. The computer I'm using to send this message shows me none of these feelings unless I press the icon buttom
He's cried and laughed. It wouldn't be Star Trek if it wasn't about trying to make Spock show emotions.
The entire basis of the McCoy/Spock banter is that McCoy is trying to help Spock release emotions in a gradual, safe manner so he doesn't bottle them all up and explode. Since the movie apparently is set around the time Spock meets McCoy, it makes sense that he's kept his emotions under lock and key and is ripe for an outburst. Spock learned a lot from McCoy. I hope the movie gives McCoy his due.