very long post incoming, apologies in advance;;
i subscribe to the opinion (lol) that ralph is upset because the conversation in the car didn't go as he had expected. i mean he drove to a romantic spot where they could be alone. i'm sure he was trying to create A Moment with laurie.
i'm using the longman's edition which i think makes things a bit clearer.
ralph was speaking in a soft, intimate voice, which causes laurie to panic and ask about hazell in more detail. i'm sure ralph wasn't intending that to be the topic of conversation.
he talks about how he was sure hazell was gay. i'm pretty sure when he says "it wasn't everybody one felt justified taking a chance with. side-tracking them, or something..." he's talking about laurie. i mean, in the study scene he says "you're on your way to being something [...] so i'm not going to interfere with it."
i think he's trying to hint to laurie how much he liked him at school. right after this he asks
and realizes that laurie is oblivious about the reason hazell hated him (jealousy of ralph's affection for laurie). then laurie asks more questions about their affair (the prop room) and then we have the "esprit de corpse" bit.
ralph learns that laurie is very much of the same opinion as him re:specialists (bonding over internalized homophobia yay!) therefore even more compatible with him than he thought, and then he says the bit about having "all you need at home."
now, i think in ralph's mind this would have segued the conversation back to laurie and ralph, but laurie of course thinks he's talking about bunny, gives a lukewarm response which obviously disappoints ralph (he "failed to follow it up") and brings up hazell AGAIN.
ralph looks vague because i think the conversation was never supposed to be about hazell, but it seems to be all laurie wants to talk about. then ralph tells him about the end of the affair and his expulsion.
at this point ralph's distressed, as shown through his tapping and his fumble turning the headlights on.
the infamous Knee Touch. they both got nearer enough to each other to "draw back." i think they were finally having A Moment after all the missteps and misunderstandings and painful rememberances, just to be interrupted in such an irritating way.
laurie is still oblivious to the depth of ralph's feelings for him (and in the '53 version he doesn't really reflect on their proximity at all afterwards), so of course he would put ralph's irritation down to not having a drink yet.
i agree with @renaultphile about laurie being pretty vigilant about how much ralph is drinking and that it may have been from having an alcoholic father. even if he was too young to pay much attention to it (michael didn't succumb completely until he was out of the picture, after all), i'm sure his mother instilled some type of attitude towards it in him. he's more mindful of it in the '53:
after the dinner conversation:
they flirt some more and ralph once again briefly mentions settling down (at least that's how i interpreted his saying "one's final choice," thoughts??) and then, mindful of having an hour left, he invites laurie back to his place 😏
tumblr's trying to silence me so i'm breaking this into 2 parts lol