Here at COACISSW we generally adhere to a strict no cutting-open-humans-and-crawling-inside-to-survive-a-storm-in-the-wild policy. However, in the timeless words of Spock just before he ventured into the lethally irradiated engineering room of the starship Enterprise, "The good of the many outweighs the good of the few, or the one."
Now imagine you are trapped in the Forbidden Forest, a massive storm--possibly natural, possibly the work of He-Who-Shall-Not-Be-Named--is brewing on the horizon. Acromantulas are closing in and the Arania Exumai spell isn't working to hold them back. And there, at your side, is Hagrid: twice as tall and five times as wide as the average man. His barrel-like chest cavity capable of sheltering your entire party for the duration of the storm.
Plus, he's half giant, so he isn't really a human at all.
Hagrid is friendly and softhearted. Use these qualities against him. Begin to cry, bemoaning your approaching demise. Tell him of all the things you wish you had done, the mountains you would have climbed, the tournaments of wizardry you would have won, the animals you would have treated more kindly, the man or woman you would have kissed. Ask him for a hug.
Sneak your blade into your sleeve and wrap your arms around his neck (be sure to get them under all that hair). As he's squeezing and comforting you, draw out your blade and jam it into his throat with all your strength. This first cut is crucial--Hagrid is quite strong. If you don't wound him terminally with the first strike he'll shake you free and stomp you to dust. Be sure to sever the carotid artery.
There will be fountains of blood. Leap out of the way. Let him tire himself out staggering around trying to staunch it. Ignore his pleas for mercy and his bellows of "Why? Why?" When he collapses, roll him onto his back, slice open his chest, remove his big warm heart, and crawl inside. The acromantulas will leave you alone safely inside their beloved friend, and the storm will pass.