Big Man On Campus is a trophy achievement which activates during a certain section of the game.
The trophy achievement itself requires you to find a knife whilst playing as Alex. This one is probably not a difficult one to obtain as long as your inspecting the different items and objects that you come across.
What also helps is that there is a feature that lets all items and objects shine and stand out, making it almost impossible to miss anything.
However, if you are struggling then the event occurs when your playing as Alex and are trying to escape from the thugs that throw you into a room on a deserted Ship.
If you continue playing as normal, you will eventually reach a Kitchen and obviously Knives belong in a kitchen. You will find it in the back of the room.
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