thinking abt illumi always using hisoka's last name whenever they're outside mainly because the zoldyck name attracts too much attention and he doesnt want that but also because hearing illumi morow makes hisoka have multiple floaty hearts above his head and woozy for the rest of the day

illumi registers as "hisoka and illumi morow" in a restaurant and hisoka starts giggling and batting his eyelashes and follows illumi to the table with heart eyes while also floating behind him cartoon style

However, when Illumi hears "Hisoka Zoldyck" it triggers the most feral parts of his brain. His eyes grow so wide for a couple of seconds it completely betrays everything he'd just felt at that moment before composing himself. Hisoka obviously takes notice of that and is like. ohohohohoooo.

He uses it to tease Illumi while theyre alone ONCE. just ONCE. and illumi pounced on him like a predator. the quickest way hisoka learned that this was not just a reaction trigger word for illumi. it was an ACTION. he just has a godly amount of self control when theyre not alone.