Loki finished the last bite of his cupcake, wadding up the paper and tossing it back over his shoulder in Thor's general direction. He sighed as though utterly put out by this whole affair, before peeking back over his shoulder and grinning. It might be better since they were likely going to be arrested if he had a much different face, so with a flick of his fingers, he created a different boring Midgardian facade that everyone else besides Darcy, Thor, and Valkyrie could see. Much easier to fool the police that way. He'd simply shapeshift into it if he had to have a photo and fingerprints taken before being locked up. It looked like one of his apartment neighbors anyway.
What would have been super easy for him was projecting one of his magical clones up there and attempting to appeal to Valkyrie's better judgment, but that didn't seem like much fun. And she looked to be having fun climbing, so why ruin it?
"Hello, brother," he said, as though talking about the weather. "Darcy was about to go forth and stop our fellow Revenger with the power of niceness. Far be it for me to interrupt."