Disclaimer: I'm sick of trying to make these funny. I don't own these characters. So there.
Harry jumped into the old Ford Anglia, with the pair of Death Eaters closing in behind him. The car had turned up at just the right moment, just as Harry was running down the empty road from Hogsmeade to Hogwarts. Shooting random Stunning spells, he accelerated and jabbed the silver button on the dashboard, which he remembered to be the Invisibility Booster. He heard Nott and Mulciber's enraged shouts behind him. Laughing, Harry sped up even faster. He glanced at the odometer, and saw the little dial reach 80 mph. Suddenly, the old turquoise car gave an almighty lurch, and stalled. Harry slammed on the breaks, and skidded to a halt just in front of those ancient wrought iron gates flanked by winged boars. Getting out, Harry realized that he didn't know how to unlock the gates.
He tapped his wand awkwardly on the metal as he had seen Snape do before, but nothing whatsoever happened. Sighing, he lowered himself onto the ground and leaned his head against the cool metal of the gates, resigning himself to a long night of waiting.
It could have been ten minutes, an hour, or all night, but at some point Harry heard loud whistling coming his way from the Hogsmeade road. Startled, Harry jumped up and yelled "Hello?" The whistling stopped abruptly.
"Who's there?" said a familiar deep voice. "Show yerself!"
Harry lit his wand, and directed the beam of light in the appropriate direction, and a large figure came suddenly into focus.
"Hagrid!" Harry sighed with relief. "I... erm…" He realized that he should not be telling anyone why he had left the school so late at night. Harry racked his brains, trying to quickly think of an appropriate alibi. "I…"
Thankfully, Hagrid interrupted him.
"James? Is that yeh?" Harry could not think of any explanation for this, and peered confusedly up at Hagrid.
"James? Hagrid, are you ok? It's me, Harry!" Thinking that maybe he had had too much to drink or was ill, he shouted the last bit.
"Harry? Who's Harry? James, what have yeh done to yer eyes? They didn't used to be green, did they? You didn't get one o' those weird Muggle things- contracts, they call 'em?"
"Hagrid, what are you talking about?" Harry was totally bewildered. He had seen Hagrid just this morning, at breakfast. His massive pal looked exactly the same as he had at 8 o'clock that morning.
"C'mon James, let's getcha up to the castle. I'm not gonna ask what yeh was doin' out here this late, all those pranks yeh get up to an' all. Why yeh haven't been expelled yet is beyond me…" Hagrid pulled out his pink umbrella and tapped the gates just as Harry had done earlier that evening, except this time there was a great clanging sound and they opened. They both stepped through and Hagrid closed the gates again, locking them tight.
Harry was completely perplexed as to why Hagrid didn't recognize him, but followed his large friend up the path towards the castle all the same.