Fred Mischief Weasley? I would not be surprised if that was true. Anything except Sir Shimmery Fred Sexy-pants? But it's such an awesome nickname!
[Private to Fred] I like when you call me Bells. I like it even more when you call me yours, though. If anyone was Mischief Managed, it would be you and George.
Let me know when you figure something out. Although you know, some of the best nicknames come in the heat spur of the moment, when you're around the other person.