Harry was grinning by the end of the interaction, knowing that George would be one of the easiest people to make friends with. Yes, he could hold grudges just like the rest of the Weasleys, but Harry knew that if someone could be friendly, then George would eventually warm up to them.
"You should have seen your face when you walked into that shop. It was like you were facing Voldemort for the first time," Harry teased, trying to get Draco to lighten up a bit more. The other boy could be quite serious when he wanted to, and Harry guessed that now was one of those times.