Miles never quite knew how to take Bellatrix when she wasn't barking orders at him - or even when she was asking him politely. She obviously enjoyed keeping him on edge.
"Daphne will no doubt be honoured by the invitation, yes." More like she would yell at him, and deservedly, for getting her involved. Right now, he didn't know if Bellatrix, or Daphne would be more wrathful.
"We await your invitation," he said, starting to get fidgety. He really was going to have to go if he were to get ready for the ball - Merlin, and to tell Daphne they had to go - in time. "Thank you, Bellatrix."
He met her eye one last time, and then turned, walking much faster out the door and hoping that he wasn't going to be interrupted by any other Lestranges.