I believe that you should definitely set your own example by not laughing or deriding that other student. If they do something wrong, you shouldn't laugh at them or mock them, but rather try to help them. What you can do as well is ask that other student nicely to stop deriding other students because of a mistake they may have made.
Ludere means to trick. Collusion is secret, illusion is a trick, elude is to avoid escape. These are not options. A prelude is an introduction - almost like a taste to trick you into reading, hearing, seeing more. An ablution is a washing - not connected to a trick at all. Ablution is your answer.
