That is the worst one. I had one back up on me when I was working at this one restaurant. So terrible, I had to go outside or I would puke. Puke is also a terrible smell.
Cool story, I saw this thread yesterday. As I glanced over it, I smelt something terrible, so I opened my window. I was going to post "what ever my room smells like right now". But I didn't, since the smell was unclear. I then went to class. Turns out, there was a gas leak on the 8th floor of my res building (I'm on the 10th). The whole building was evacuated during the time I was in class. I finished class just as let everyone back in. Firetrucks and Hazardous Material trucks were there and everything.