The best one I heard was from someone helping to run an undergrad practical class -- she forgot to specify that when using a pipettor one should use the disposable plastic tips and not just dip the end on the Gilson directly into the solution. And I guess it *is* a valid point if someone has never seen a Gilson before but, *man*.

Of course, however good the instructions are you still can't do anything about the people who don't read through to the end of the protocol before they start work, or that if pieces of equipment don't seem to fit together then brute force is a better option that checking they're going about it the right way, or who think than ammonium sulphate and ammonium persulphate are probably close enough.