[Don't look at him like that! It's not like he thinks it's hilarious that what he says and what he means aren't at all the same.]
What’s your meaning, boring mumble? Disapproving, do you grumble?
[Did he just insult Kirk? He thinks he did. Chekov shuts himself up and results to miming, pointing at Kirk, then himself, and then gesturing forward. That's supposed to be an invitation to join him on his run. Since mimes aren't native to Russia, that may not be entirely clear.]