Hi, I’m speaking on behalf of my translator: “Perhaps you’re right about it being a weird choice. He used a variation of ‘stupid’ yet to be used before (ボケナス/Bokenasu) and I was just trying to diversify. But, at your comment, I’ve looked into it more and brainlet is far more online than I...
Sen’ichi’s full sentence is: “I’m number 3 at Club Trillion’s ex number 3’s club!” hes lying about being number 3 at Club Trillion to get out of fighting that guy by only saying the first part out loud.