The trick to getting permission for anything is finding is finding a person who has the authority to say "Yes." Most of the people that you encounter, secretaries, janitors and the like, have learned that saying "No." never gets them into trouble.

The "younger guy" who gave you the 3rd degree - did you ask who he was? Introduce yourself and offer to shake his hand. If he's not willing to do that I wouldn't worry about him too much because it shows he's insecure about his actions. More often it leads into an objective discussion of the potential problem they are trying to resolve and ultimate permission to do what you are asking.