Especially at the dentist.
Today I had the privilege of having a root canal at an Orthodontist while still a bit under the weather. The result: a violent sneeze during the procedure.
Luckilly, I was quick enough to raise my hand in warning giving them a chance to remove the fine drill from my mouth hole. Basically, I almost blew the thing off my face, got snot all over the outside and filled the back of said dental shield with viscous sputum.
It was so awesome.