It has happened outside CNN offices in Manhattan before. At the time, "Anderson Cooper 360" would often air on the ground floor with a large, extremely thick window separating the broadcast room from the outside world. This was a nationally syndicated show that had a broadcast/camera room with a gigantic window right behind the host. The show was not on any significant delay that I know of, and was aired live. There seemed to be a 20-30 second or longer lag, but nothing significant. Often times people would come by and wave with their boyfriend or girlfriend. I did it at least once around 2003 (ahh.. the days when I still had a steady girlfriend! ).
Being a news junkie at the time, and after we spent time in the spotlight, whenever I saw the show on television I would start to pay attention to the people near the window. Most were tourists trying to reach family to tell them they were on TV. Sometimes there were Iraq war protestors outside the window holding up signs, or a group of people all wearing the same outfit. On rare occasions, you'd get someone giving the middle finger to the cameras. Every once in awhile some nutcase would streak across the window. Most would just pass by and wave or stand and stare at themselves on the delay. Others would wear t-shirts with some message. Whenever streaking happened, it is my understanding the network started being fined by the FCC (Federal Communications Commission) a significant amount of money.
At the times we passed by, they always had a security man guarding the window. However, there was no way for him to stop people from just walking up. Also, the show could sometimes be seen right outside on larger LCD/plasma screens at the time.
Eventually, it got to the point where sometimes people would walk right by naked with writing scrawled on their chest, etc. This made the news on other channels a few times. I assume this is why they moved operations out of the ground floor, or as one rumor goes, simply added a background to cover the window, and you do not see many shows like this done that way anymore. When they are done this way, there is usually a road block set up so you can't get too close to the window, or get anywhere near it at all. Still, people in the distance, even across the street, will clamor to be the backdrop/wallpaper on cable news, even for a few seconds.
I've never seen someone go crazy like that though I bet it aired.