Rukia asked Renji why he always tied his hair up.
He told her that it was because his hair always got in the way of everything. She didn't quite believe him, and dared him to keep his hair out for an entire day.
He reluctantly agreed.
For that day, Rukia observed him and scrutinized him and his actions carefully. She was surprised.
When he ate, it seemed as if the food had been magnetized to his fiery locks, and he ended up biting some hair along with his bread.
When was running after a hollow, the hair blew into his face and tickled his nose, causing him to sneeze an awful lot. If he hadn't been accidentally bumped by the hollow's tail, he probably would have crashed into a building.
During a nap, Renji slept with his hair messily strewn over his face. The strands went into his mouth and he woke up in a coughing fit.
Even when he simply sat down on a bench, the wind blew his hair into his face, so his world was streaked with reddish-magenta stripes.
It was amusing, but it was dangerous. At the area where Renji was sitting on his bench, some kids were playing ball. The hair in his face didn't allow him to see the ball coming and he was creamed comically in the back of the head.
Rukia had to cut the dare short, and quickly tied his hair back into its usual, sparky ponytail.