Here is one that was pretty stupid. I used to work for IBM as a Engineer. We were having the equipment tested with infared cameras to detect hot spots and loose fittings. These guys come with equipment that looks like there right out of ghost busters. Were walking to one of the equipment rooms and a lady says OH My what are you doing. JOKINGLY I say oh were testing for radiation the building is built on a toxic waste dump. or something just like that. Just joking....but kept on walking. 5 min later the fire bells go off and they evacuate the building..hehehe We were always playing jokes there and this comment was just a joke and that news spread threwout the building in less then 5 min and the place was evacuated. A memo had to go out explaining the contractors business and what they were doing. Needless to say we mellowed a little on the jokes for a while.
