Harry was running just a few minutes late, having been kept after class by Williamson for some form of interrogation. At least, that's how Harry viewed it, and had uncomfortably answered questions without really knowing why they were being asked. For instance, he didn't know why Williamson needed to know what kind of music Ron liked, unless it was a sort of test to see how well he knew his other Auror trainees. There had been questions about Draco, Justin and Susan, as well as several others, after all. It was just...the questions about Ron had been more...personal.
He'd finally been told to go, and had rushed home to get ready for Justin's party. He was slightly (okay, majorly) disappointed that Ron had apparently left without him, and thought about not going at all, because clearly Ron didn't want to be around him tonight. Then, telling himself he was being ridiculous and was clearly low on sleep and logic, dressed quickly and Apparated to the Leaky Cauldron.
He didn't notice until he was almost there that he was wearing two different shoes, and a shirt he'd stolen from Ron somewhere along the way and jeans that were just barely held together at the seams. They were also several sizes too tight, but he must have been so preoccupied with the interview and Ron's abandonment that he hadn't noticed. He hadn't even remembered robes. It was too late to return home now, so he just hoped no one would notice, and that fancy dress wasn't required.
Squaring his shoulders, he arrived at Mad Gurdy's and headed inside, spotting Ron immediately. He made his way over to the small crowd, and before he knew it he was saying, "I can't believe you left without me Ron! I was only ten minutes late getting home!"