It was pretty simple conversations such as: Yes, I have a drivers license and a car but, I choose to ride my bicycle. I like to commute on my bicycle because...(insert reasons). This is my primary means of transportation to work.
The sticking to your guns: I am going to be washing up and changing here in the bathroom everyday at this time. My bicycle is just as valuable to me as your cell phone, purse or wallet is to you; this is not a toy (pointing to the bicycle). Understand that your job (the security officer) is to protect the property and my bicycle has just as much value as the people and building. My bicycle clothes are necessary, would you drive your car without a windshield?
These are a few examples.
It was not easy at first I heard everything that others have heard, the you can't park your bike here, you can't wear lycra in here, you can't change in here, etc..