okay so the lancetris ones are not as plentiful and defined as the melban ones, but heres what i got :3
Melban
Ban makes all of his meals with Meliodas in mind. He doesn’t care much if the others don’t like it - he wants to see if Mel does, and if so, he adds it to a little ranking he keeps in his head of Mel’s favourite dishes. He will never admit this to his face though.
They are both extremely crow-pilled. They gather and gift little trinkets all the time (usually pretty, shiny, and sparkly or metallic things). They each have a seemingly bottomless chest, courtesy of Merlin, in which they keep their gifts.
Ban has a collection of various knives and daggers given to him by Meliodas - they’re super varied and span across many cities in Britannia which Mel visited during his missions. Ban treasures these a lot and loves looking at them and playing with them.
Ban learned how to make flower crowns during that first week he spent with Elaine, and now he makes them for Mel when no one else is looking.
Ban is not immune to Meliodas’s pervy groping - Mel will take any and all chances possible to grab at his chest or ass (the latter or which is rather easy to do considering the height difference). It’s a gamble whether Ban will just stay there and take it or if Mel will get punted into the ground
Meliodas (in assault mode) is responsible for all of Ban’s piercings (doing them normally always ended up in the wound closing and rejecting the piercing :( )
they get freaky with it, 100%
Meliodas will often flop himself over Ban’s shoulders while he’s cooking; scarf-style.
If either of them makes a flirty comment towards the other, it will start a back-and-forth of increasingly blunt and explicit comments until either one of the others Sins breaks it up, or they start making out.
Lancetris
There have been more than a few instances where their duels/fights have gotten very up-close and homopilled; what followed remains a “mystery”
Lancelot is the biggest tease out there but acts like he has no idea what he’s doing, which successfully gets Tristan flustered ~100% of the time.
Whenever Lancelot trains, he often does it shirtless, and the sight makes Tristan’s face turn bright red. He’s not complaining about it though. (Lancelot knows what he’s doing, once again).
Lancelot is not one for PDA, but he does get very clingy in private, though you will never see him admitting its because he loves the physical contact. It just so happens that he wanted to be in this exact space independent of Tristan being there. And you better not mention anything about the fact his entire body is wrapped around Tristan’s.
Tristan finds Lancelot’s Sin form adorable, and he insists on Lance switching into it every now and again so that he’s able to provide more efficient and well-encompassing hugs.