Biff grabbed the note. Not because he wanted to read it, but because his curiosity of the "magic note" outweighed his common sense.
And when the note got close enough to him, Biff felt compelled to read it. "I wish that the last person who teased me would do anything to become my best friend."
Immediately after Biff made that wish, Randy Goodman (the last person who teased Biff) suddenly felt dizzy. Soon, he would do anything to be Biff's best friend. It was kind of funny, though, because from Biff's point-of-view, Randy was already his friend (before Biff turned into a geek, that was).
