Doctor/Dentist, Bands, and Mirrors!
He sure as hell isn't going to be one. He avoids them because they keep telling him to live in a more healthier way - kaiji loves alcohol, sweet stuff, smoking and then there's his lifestyle in general. He just shouts them to stop giving him advice and getting over with the check or whatever.
I can totally imagine Kaiji getting horrified about going to dentists, probably lingers several weeks until the toothache gets so bad he can't do anything but cry about it. He can't really afford to even go to one right now tho...
in the end he just ends up getting so tense he's confused when it's all over.
I can also imagine this dentist scene in the style of the series tho INTENSE SHOUTING NARRATOR and zawas everywhere....... (well there IS A DRILL, two kinds of drills actually, in the series but those are a little worse than that)
Listens to punk rock and that kind of stuff haha, I'm not really familiar with the stuff myself but he actually has some band T-shirts about bands that actually have existed like The Blue Hearts (who sing the full version of first Kaiji OP! Also they sang Linda Linda) and the High Lows.... (tho i think the latter was formed after the previous broke up idk the dETAILS) so yeah! I can completely imagine Kaiji getting really excited about bands haha. He thinks band shirts are hardcore and so on, yeah.
Probably starts tidying his hair when he sees one haha... He probably even poses in front of the mirror trying to make tough faces. In the morning he just tries to avoid them except when shaving and all that. Kaiji IS despite everything pretty clean person. (He probably washes his hair at some random public toilet.)
But yeah, also stares at them when getting all reflective... Kind of seems to remind himself of nothing but yeah just can't put finger on.