Rectal thermometer jokes

Someone asked me what the worst mistake you could make while being at work was, and I replied, "Being a doctor and mixing up the oral and rectal thermometers."

I reached into my pocket and pulled out a rectal thermometer and thought,

"Some asshole has my pen!"

What's the difference between an oral thermometer and a rectal thermometer?

The taste!

What's the difference between an anal and oral thermometer?

The taste.

The doctor told me my temperature was exactly 98.6 degrees. I felt relieved until he said, “Celsius.”