He was forced to let go of Captain's collar when Captain shoved him, due to Captain's greater arm length resulting in his head being bent back. He didn't bite, partly to avoid being bellowed at again and partly because he was sure whatever dirt he'd just had rubbed on his face was radioactive.

"Bwah, you're disgusting!" He pulled up his sweater and scrubbed his face vigorously. "Use a sink once in a while! The world doesn't clean you here."

He tugged his sweater down again to glare hotly as soon as he'd replaced Captain's muck with streaks of engine grease, threatening him with a fervent "I'll get it soon! And you'll thank me when I do, because if you do that to anyone else, a bruised jaw is going to be the least of your worries."