Regulus has managed to be very pleasant to everyone, which meant not actively insulting the Weasley girl and Remus' son, and he had to remind himself the last part, or the insults would have started a lot sooner, but he wasn't in the mood to stay quiet anymore.
"Severus is right, this was wonderful, but then we didn't expect anything different from of a woman of class such as yourself," Regulus said with a smile, and then looked at Weasley. "Too bad that not everyone has the same class. A woman with the right pedigree would know when an invitation should be turned down and spare everyone her presence."