This has only happened to me once. And if it ever does happen to you, you won't forget it.
I was having a casual conversation with a guy in one of my classes (I was in college at this point.) He had this massive whitehead on his nose. Only it wasn't only white - it had a green tint to it as well. It was the nastiest thing I'd ever seen on any face in my life. After a minute or so, I couldn't even look at him. I was just like, 'm hm... uh huh... yeah...' Disgusting :/.