Spock brings Jim to New Vulcan (as friend) for whatever reason. Some Vulcans are insulting Jim since he’s human (Vulcans gave Spock a hard time for being half human so just imagine how they would react to a human.) which upsets Spock because Jim is his friend cough and future boyfriend cough. But Jim speaks the current language of the Vulcans and Old High Vulcan (”I got bored with modern Vulcan.”) and knows exactly what they are saying about him.
The insults don’t bother him so he just shakes his head at the Vulcans and plays a dumb blonde human since he likes people underestimating him. (All the while Spock Prime finds the whole situation humorful. Vulcans, in arrogance, are calling his younger self’s t'hy'la dumb when their arrogance makes them blind to fact Jim knows exactly what they are saying.) Then some Vulcan decides to insult Spock and Jim tells them off and insults them back much to everyone surpise (excluding Spock Prime).