okay so first off: sorry for getting to this message over a week late. i wrote out this long answer based on a complete misinterpretation of what you were asking i’m going to be completely for real here. i want to start off with saying that it is really dependent on who akihiko is talking to. inherently akihiko wants to be this cool-headed, reliable figure for people, especially those younger than him, so he naturally tries to conceal any hint of playfulness and immaturity in most cases.

i also have to clarify before i get to the meat of my answer that i don’t really see akihiko as “childish”, even though he can have attitude. i say this because a lot of the portrayals that i really dislike are the ones that overly exaggerate his childishness. some dialogue additions in reload (specifically the added lines about mitsuru having to micromanage him) reflect this trend in his spinoff characterization, and to be honest it just rubs me the wrong way when it’s played like he’s not incredibly self-disciplined and responsible.

anyway onto the actual question. a lot of the best examples of akihiko’s banter/sass/etc. come from the drama CDs. you’ll find that when it comes to his general responses or demeanour, akihiko is pretty blunt in tone. there are a few instances in-game where akihiko makes kind of lame jokes that don’t really sound like jokes because of how he’s saying them, and sound more like dry observations. this is how akihiko’s humour comes across in most scenarios, when in the audience of underclassmen or people he’s not very familiar with and where he’s not comfortable enough to really be especially personable. again he strives to look level-headed, and this presentation only really drops when he’s challenged (i.e. in operation babe hunt) ^_^

still there are varying extents of his dry humour. for instance, in character CD volume 3, akihiko (upon seeing shinjiro has been minorly injured) flicks the bump where he’d got hurt, while joking that shinjiro’s face “looks like dried up jerky” (referring to how wrinkly he looks from being irritated). it’s pretty apparent that akihiko wouldn’t really joke like that with anyone who isn’t shinjiro (we never, for instance, see him poke at mitsuru — the most there is him calling her a “random rich girl” in the reload version of the answer, but this line doesn’t make any sense given he’s also rich), given he explains in the same dialogue what shinjiro is feeling.

this is a tangentially-related note, but as someone who’s been into this series for some time before reload came out, i will say that i really disliked the way reload portrayed their dynamic in shinjiro’s linked episode. it really feels like akihiko doesn’t know even really know shinjiro with the shit he says, when all other media points to the opposite being the case. even junpei remarks that akihiko is “only able to read [shinjiro]”, and it’s remarked by several other members of SEES how well they know each other. akihiko’s familiarity with shinjiro is likely why he’s so comfortable teasing him. you’ll really only see him make smaller jabs at junpei, which happen more the later on in the game you get (especially related to his studying habits and motivation), as a result of the fact that he’s more familiar with how junpei feels about those kind of remarks.

as for his attitude, akihiko’s stubbornness plays a big part there. he strives to be independent and doesn’t like being bossed around when he has his own opinion of how he wants to do things. akihiko’s stubbornness usually results in him wanting to dispute any infraction on his character, often on petty matters (and on losing battles, as i’ll talk about later). in character drama CD vol. 5, akihiko and shinjiro’s argument (of which the plot of the CD is based around) spawns from akihiko not responding to orders to flee the fight and endangering the group as a result. akihiko also usually disputes any dismissal of his ideals and mentality, like you see with the drug confrontation, but this is less about his attitude and more just another way his stubbornness manifests.

there are a few good examples in Q of akihiko’s attitude, but Q overall really leans into akihiko being more childish (with he and shinjiro often diving into not just petty but genuinely childish disputes when they’re left alone for too long) among Other things i hate about its characterization of akihiko, so i can’t recommend it too much. he does “hmph.” shinjiro once and that was really cute though. he’s not above giving the silent treatment. if there's anything i would recommend watching, i'd say a video of Q2’s ticket #19 – transcendental trust is worthwhile. it has cute interactions centring akihiko/shinjiro/mitsuru/kotone, and shows off akihiko’s competitive banter with shinjiro as well.

i’d say the petty side of akihiko’s stubbornness is best epitomized in the episode rain drama CD, where akihiko and shinjiro have a back and forth where akihiko tries to argue against the fact that he was scared of storms as a kid. eventually, akihiko concedes that shinjiro is right, mumbling that it wasn’t the lightning that scared him, but the thunder. a similar exchange happens later on in the same CD, where akihiko tries to argue that shinjiro didn’t look after him when they were younger before shinjiro threatens to bring up examples (whereby akihiko then surrenders). i actually really recommend episode rain for showing the more endearing side of this trait. he has attitude throughout nearly the whole nine minutes of it.

the drama CDs generally offer genuinely pretty nuanced snipits into akihiko’s character (well, every one except “a certain day of summer” since that one is a comedy CD). his other two major appearances are in character drama CD vol. 5 (which i know i already mentioned, but still) and the seaside vacation before death’s scythe CD. character vol. 5 centres akihiko and shinjiro having and argument and then the process of them making up; it’s one of those things that when i first listened to it i fell in love with akihiko’s character all over again. it focuses more on both their respective stubbornness, and while it doesn’t highlight akihiko’s attitude/playfulness, it does show off his character and the compassion he has for others (and shinji in particular coughs), so i still wanted to recommend it.

as for seaside, it’s where you’ll find a lot of the more casual banter between him and shinjiro and him and mitsuru. there’s no real arguing in it, but a lot of more fun back-and-forths. i highly recommend it — it’s also the only media that actually explores the group dynamics between the three of the first year SEES members during their first year.

i generally don’t advise the daylight/moonlight drama CDs insofar as giving a good look at akihiko’s character, since it doesn’t involve too much of him. still a really nice one overall and elaborates on group dynamics and aigis’ character. i only mention it here because it has a couple of instances of akihiko being more playful (again with shinjiro). notably he whines about how shinjiro doesn’t cook for him (reminding him later on about this when shinjiro agrees to cook for ken), gets excited about the typhoon (to which shinjiro calls him a “brat” for), and also nags the hell out of shinjiro to come to tartarus. i tried not to include any specific dialogues in my response but i don’t recommend going through the whole of daylight/moonlight just for akihiko interactions for the above reason (he’s not a central figure), so here.

⠀⠀⠀⠀Sanada: Hey Shinji! Why don't you come too?
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀... Huh? Where'd he go? I was sure he was here until a little while ago...
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀Hey, Shinji! Shinji, come on, answer!
⠀⠀⠀⠀Aragaki: Shut up already, I can hear you just fine.
⠀⠀⠀⠀Sanada: We're heading to Tartarus tonight, so get ready.
⠀⠀⠀⠀Aragaki: Fine.

anyway, those are my notes on how akihiko’s less formal attitude and banter manifests. generally, while you don’t see it too much in game, the drama CDs add a lot to akihiko’s overall character and they’re what i mentally reference the most (outside of the actual game) when i write him. i would also recommend persona 3 dancing’s socials if you’re interested, because they also more akihiko interactions with various members of SEES occurring later on in the game’s cycle (P3D is set in january 2010), where he’s more comfortable with people. it’s clear in that game that he’s let his guard down a bit and banters a bit more with each of them.

lastly, thank you so much for asking and for loving my idea of akihiko. it means a lot to me as i really love this guy <3 i hope that answer helped clarify!