Said intern did in fact shit all over the 18th and 25th floors of 30 Rock. She did it in the hallway, on the floor, on a pile of FedEx boxes, on the way between floors… pretty much everywhere but the bathroom or (hey, sometimes you're desperate) a garbage can. Or a cup. Or a napkin. Or in her hands. No, just streaking through the hallways. And then she took it into that room where she locked herself in and proceeded to wipe (sorry, I couldn't come up with a better word) it on the walls, on the computer, on those same FedEx boxes. It was a shitshow (pun absolutely intended).
The intern blamed the mess on bad water that she drank in Israel (although she had been back from her vacation more than 2 weeks before she started). The rumor at NBC is that it was some kind of laxative induced disaster.
The bosses did want to fire her but were so shocked that she came back that they were a little scared because, what kind of person does something so gross and then shows up the next day like nothing happened? No one wanted to bring it up again, so she got to stay by default.