Hermione was just scary, sometimes. Organized, thoughtful, brilliant, dedicated, brave, and caring - but terrifying. "So you just saved up hairs? How do you have them saved? A baggy for 'blond tall bloke' one for 'balding short man'?" he asked, teasing a little. "We end up doing this much, how much you want to bet that with our luck we'll just stroll face-first into whoever's hair you plucked and leave them staring at themselves?" Which would probably be more bad than funny, since they'd have to be obliviated, if they were muggle, and then the Ministry would know someone was running around polyjuiced. . . but it was still sort of a funny thought. "Didn't anyone yell at you for grabbing at their hair?"
"We can always get more while we're out too. Just assault random people to yank out their hair. No one will mind." Harry was smirking and couldn't quite help it. Imagining Hermione rushing after people and trying to stealthily pluck hairs was just more fun than thinking about running off to the graveyard his parents were probably buried at.