HAIKYUU HEADCANONS!!

Their bad habits

-Atsumu Miya

Eating up your food. And he's a hypocrite on top of that. 
"Y/N, did you eat up my pudding?! I was planning on eating that today!" You scoffed as you heard your boyfriend's yelling from the kitchen. "Didn't you eat up my food from the fridge on Wednesday? Okay then." The audacity of this man. Now you had to suck up the fact that Atsumu was inevitably gonna be pouty all day but you weren't gonna baby him since he eats up your food all the time. "That was Wednesday! Today is Today." He stomped to the living room, arms crossed as he looked down at your annoyed expression. "Tsumu.. you complain about the time I ate your cookies everyday. It happened last month." 

-Shinsuke Kita

Waking you up in the morning with loud ass cleaning sounds like POC moms on Sundays.
"Shinsuke.." you groaned, rubbing at your eyes as you step out of your room. "Hm?" Kita looks up at you, his hand continuing to scrub at a pot in the sink. He rinses it off, placing it down, the pot making a loud, lingering sound. "You can't do this after I wake up?" you look up at him annoyed. He simply tuts and shakes his head. "You always end up leaving behind a mess at night so it's my job to clean it up in the morning."

-Rintarou Suna + Kenma Kozume

Staying silent when there's an issue. It's not like when they're mad, especially Kenma, he'd make sure you know he's irritated but it's when they're upset or sad about something. If they're hurting, they're most likely not gonna tell you and just find a way to distract themselves about the issue since they're reserved about their thoughts.
(that got a lil angsty, my bad)

-Yuuji Terushima

If you wear masculine clothes that fit him, he's gonna wear them without permission. "I have a date and I forgot to do laundry last week, sorry!" I feel like it'd be okay though because he wouldn't mind you taking his hoodies and oversized shirts, platonic or romantic relationship.

-Keiji Akaashi (more angst)

Overworkinggg. Akaashi would probably work hard for the both of you, trying to please you more than he pleases himself. He'll try to take on a lot of roles in your shared place even if you insist to do them. You'd have to sit him down and be like, "Keiji. That's enough, please rest."

-Tetsurou Kuroo

Provoking people he doesn't like that you like. Scenario time, imagine Daishou talking with you and Kuroo takes it as "he's trying to flirt with them to get back at me." He'd immediately go up to the both of you, pushing y'all apart and giving Daishou the most passive aggressive smile ever. Kuroo would make it look genuine too but the both of you can tell he's trying hard not to bring up info he can blackmail Daishou with.