SPOILER:
I get what you mean, but I think the writer did that on purpose to show another side of him.
He like that cuz he's drunk—some ppl's personality can flip 180 when they drink.
Also, D12 is actually important. Even though it looks like a fun date, it's literally him opening up about a part of himself to MC—how he used to do "dirty work" just to survive since he was homeless, jobless, and falsely accused of a crime he didn't commit (Lars Ep).
At the beginning, he was alr ashamed in front of MC, like when he camped on someone else's property or volunteered just to get free meals. That's why MC learning more abt him in D12 is like opening a can of worms for him.
So after the date in D12, being in a vulnerable state, you can see how he tries to act normal—awkward and "out of place"—cuz he still working on accepting that past, and he's also afraid that MC might hate him for it. That's also why, if you didn't gain enough points, he will not invite you on a date.
But all of this is just my speculation, so take it however you like.