Devrait pas nous fâcher

Apparently it means "You shouldn't get us mad". Indeed, mad students are not a pretty sight at the best of times, witness this:

Is this a student or a student's grandpa, we'll probably never know. And if he is a student, what is his major? Remedial Basket Weaving 101, suggests gnotalex. Trying not to be an ageist (which I could hardly pull off, myself being decrepit to the utmost), I would suggest archeology.

But you knew I would.