I assume you're asking why I'm the "Big Cool Guy". Please allow me to slip into conversational mode and explain...
Back in 2000, Mel and I went on a holiday to Thailand. We went on a bus tour to the famous bridge on the River Kwai. We were walking across the bridge together but Mel decided that the chances of slipping and ending up in the river were a little too high for her liking, so she went back to wait for me and I continued. Exit one witness to what would occur.
I guess I looked like my version of a tourist: shorts, t-shirt, backpack, camera, cap, dark sunglasses, long hair... and tall. About two-thirds of the way across the bridge I said hello to a family of Asian tourists and I continued walking. A few seconds later I heard two of the children following me saying "Mister! Mister! You take photo?" So, I said "sure" and went back. I reached out to take the camera from the father so I could take a photo of him with his family. He said "No! No!" and gestured to his children. So, I had my photo taken with the eldest daughter, then the middle daughter and then the youngest daughter...
Then both parents came over to have their photo taken with me and the eldest daughter took control the camera. As she looked through the viewfinder she said "Ah, yes! Big Cool Guy!"
I continued my bridge crossing and when I returned I told Mel the story - never having had any sort of nickname, I was pretty impressed. However it was never going to impress Mel, who pointed out that "gai" is the Thai word for "chicken" and they were probably referring to me as the "Big White Chicken" or similar. We did discuss the possibility that I could become a tourist attraction, much like the Big Banana or the Big Merino, and tourists coming into Canberra might stop for a photo with me.
I emailed the story home to my work colleagues and forgot about it.
However, when I arrived back at work various people casually referred to me as BCG or Big Cool Guy... and I guess it stuck.
... and there is the legend of the Big Cool Guy... and you didn't even have to buy me a drink to hear it!