You are a kid. If I want to call you that, I will.

By saying that the university is "trumping" city law, you are saying that city law grants you the right to lock your bike there. The best possible interpretation of the city law that can be placed on it is that you are permitted to lock your bike to there as long as you comply with all conditions. Under NO interpretation are you guaranteed the right to leave it there. Therefore, there is no city law being trumped because the city's permission to leave the bike there is not absolute.