The city on the edge of forever: or the one in which Jim is having trouble with his feels about Spock’s hands.
He’s like “Yumm Mr. Spock what gorgeous hands you have there, so manly, yet so delicate and capable of amazing stuff and—- OMG James Tiberius Kirk, stop staring”. But Spock notices and thinks to himself "Was the captain just staring at my hands?".
Jim then proceeds to pretend there’s something really interesting in the other direction and looks there intently, thinking he totally nailed it.
Until Spock gives him this “You definitely were staring at my hands just now, were you not?” look, and Jim decides they should just jump into that Time Machine Thingy and get over with this awkward situation.