Severus sneered at Black's transparent attempt to be "charming", but he didn't yank his hand free of Minerva's. There weren't many people outside his family he would allow to touch him, but she was one of the few he didn't mind.
Fortunately, he was spared the necessity of a response to Black's comments - which would have been testy at best and vitriolic at worst - by Remus and Potter's simultaneous arrivals, and he turned his attention to them instead.