For 40 something he definitely lacks brains, self-respect and character reading.
I'm a bit younger than him but:
1) I would not party up with someone younger than 25
2) I would not form a party with people who hide behind my back without asking, they put an old man potentially in a tough spot (being kicked in the face) if he wasn't strong enough? Bystander got punched for no reason, shows their character a lot
3) I'm not desperate to be swayed by women pleading to help them out with WORK and i'm sure as hell not pedo or so desperate as to be swayed by 2 bratty girls
4) Making the arrangement that is good for both of us (me going solo and them doing their 7 day waiting period) if our schedule's do not align it is what it is. But by getting pissy about this arrangement? Yeah all arrangement's are off.
I dislike how mangakas portray people older than 20 and especially people who are over 30 or 40. Most of the people of that age have some wisdom, self-respect and self-preservation. Also anti-bs tolerance is lower, i don't like it? I freaking won't do this unless it's written in my contract that i agreed prior to start an activity.
Not every adult has what i described but majority gain it with age. In short: You don't give a fuck (not in standoffish way), and your bulshit tolerance is lower once again because you don't give a fuck, offending someone you don't really care about because they tried to sell you a bullshit idea, yeah ignoring or saying fuck you are somewhat warranted.
EDIT: My statements are based on my whole surroundings (friends, colleagues and family). I just can't imagine even 1 of them doing the same thing what MC has done or agreed to do. They are all ranging from 30 to 60, i could imagine my small cousins in their teens or 20's agreeing to those arrangements but not someone who had a life experience and bs.
And the argument about him being Japanese also doesn't hold much water, they are polite and conflict aversion orientated but not doormats. They also have more rigid seniority hierarchy, so allowing someone young to act haughty wouldn't be tolerated much.