Best student was definately a page three model!
Worst.... Not a student, but a revalidating PPL. Too many terrible things to list here, but I must say I've never sworn at one person so much
The best bit was that after scaring the living daylights out of me for over an hour, he then argued when I refused to sign his logbook!!!! Needless to say, he was gently persuaded that he would no longer be welcome to fly our very expensive, brand new a/c.