Neville blushed, though it was fortunate that he'd stumbled into Parvati's flat rather than, for example, Draco Malfoy's.
"Er, sorry Parvati," he said, straightening up and casting a quick cleansing charm on any soot he'd managed to spread about. "Something must have gone wrong with the Floo system. I didn't mean to barge in on you."
He was just thankful she was a friend, and probably wouldn't hex him too hard for intruding.