(For the sake of not being pervy, let's assume he's at least 18)

-You walk into the bathroom and he's coming out of the shower

-He is stunned for a second but recovers quickly

-Says "oops," and grabs a towel

-You didn't really see much

-You both decide to not mention it again

(Kil is also 18 here)

-You have something really great to tell him so you burst into his room without knocking

-He's totally naked and flexing in the mirror looking at his biceps

-He jumps 10 feet and turns bright red

-You beat a hasty retreat and completely forget what you wanted to tell him

-You come by his place without calling first

-It's early in the morning

-You decide it would be fun to surprise him so you let yourself in

-He's naked and hunting around his living room for something

-When he sees you, he says "Oh God, excuse me" and goes back into his bedroom

-He tells you later he was trying to get dressed and couldn't find a specific item of clothing

-It's not a big deal to him that you saw him nude

-You're in his kitchen

-He doesn't know you're over

-He comes into the kitchen naked and opens up the fridge

-"Bedtime snack?" you say

-He startles and turns around, then starts laughing

-"Check it out!" he says

-Hisoka is taking another one of his full-on look-in-the-mirror showers

-You walk into the bathroom and begin conversing with him

-You do this all the time

-He's an exhibitionist and you've already seen him naked about 1000 times

-He just washed his hair and it takes forever to dry

-It's a hot day so he decides he'll sit outside on the patio and maybe it'll dry quicker out there

-He's in a towel, but when he gets outside, the sun feels so good he unwraps the towel and sits on it

-He forgot you said you were coming by to say hi, and dozes off in the warm sun

-You stumble across him

-Everything is on absolute full display

-He opens his eyes and calmly rearranges the towel

-Asks, "Is my hair dry yet?"

-Just finished showering and is in a towel fully intending to get dressed

-His phone beeps and he looks at it

-Someone has texted him something super important and as he digests it, he forgets to hang on to his towel and it falls off

-He continues to concentrate on the texts fully nude, not even noticing the towel dropped

-You walk in

-He looks down at himself and says "Oh."

-It's hard to catch Feitan naked

-He's always head-to-toe wrapped up in his coat and mask

-You always wondered what was going on under there

-You sneak to the bathroom while you know he is showering

-You open the door and take a good long look at everything he's got

-He notices you and lifts an eyebrow, but doesn't say anything

-He returns to showering and ignores you

-You suddenly feel scared about how he's going to get you back for this

-He likes to sleep naked but nobody knows this about him

-You come by to say hi one day and are told he's still asleep in bed

-You want to surprise him so you run into his room and jump on the bed

-You realize, OMG, he's totally nude!

-You start laughing

-He wakes up and rubs his eyes crankily.

-"So what?" he says