...came back positive. We will not be hiring you."
"What? No way! How can that be?!?"
"Well sir, the container you just handed me isn't the one I just gave you to pee in."
Or
"Well, sir, the temperature of your sample is 78 degrees...that's room temperature. Takes a while for a corpse to hit room temperature."
Or
"Well, sir, temperature of your sample is 125 degrees. Either you're dead or your hand warmer is malfunctioning."
Or one of my personal favorites.
"Well sir, unless you can prove that you are a canine, we'll have to assume you were tampering with your test."
True stories. Sometimes I just have to shake my head.