If there hadn't been a child on his shoulders, Thor would have shrugged. Bodily fluids were a hazard of the job of being a father. Puke, snot, blood, bile, those were pretty much par for the course. So a little bit of phlegm hitting his skin was no biggie.
Though he was a little concerned about the fact that it was kind of cold. Which meant, of course, that it had been hanging out of her nose long enough for it to lose body heat. How much was in his hair?
Then a thought struck him, and had him carefully digging into his pocket, gently so as not to dislodge Shiloh. A moment later, he held out his cell phone to Loki. "Get a picture. Up angle, so you can get a really good shot a' the booger."
Grinning, he told Loki, "I'm gonna text it to 'Kasi. Tell 'er I should get hazard pay."