Itachi hates pounding.
The knocking on his door can only be described as pounding.
It frazzles his nerves in the early morning, at 6am exactly, because is the what he sees when he first opens his eyes. Itachi has his clock on the desk right across from his bed, because he likes to know what time it is when he wakes up. He also likes his house to be quiet, but it's clear that's not happening this morning.
Whoever is pounding on the door repeats his pattern. Three knocks, then two. Scooting out of bed, Itachi thanks himself for having the doorbell removed. His eardrums might bleed if he heard it ringing at this hour.
Begrudgingly, he slides open his closet and pulls out two random articles of clothing- a t-shirt and a pair of jeans. He tugs them on at the same time and heads for the front door.
Ah! Itachi winces. There it is again. So loud. His door's done nothing wrong, is whoever's out there hoping to punish it by pounding so hard? He pulls down two of the blinds on the door's window, peeking outside. Oh! That's who it was. Eyeing the bright orange hair and piercings on the man in front of him, he opens the door and says, "Come on in."
Half an hour later, Pein's clothes are strewn across Itachi's bedroom floor. Itachi's own freshly worn outfit is folded over the edge of a chair.
As Pein pounds into him from behind with all he's got, Itachi decides that maybe he doesn't mind pounding that much.