Similar one I did to a colleague just this summer. Went into the menu of their monitor and turned green all the way up, red and blue all the way down. They spen

Similar one I did to a colleague just this summer. Went into the menu of their monitor and turned green all the way up, red and blue all the way down. They spent a day trying to debug their Ubuntu, swapping out cables etc. and were about to go order a new monitor when I had to confess.