What's the difference between an oral thermometer and a rectal thermometer?
The taste!
Oral vs. Rectal Thermometer
Explanation
Explain Bear
Listen up, buttercup. The joke plays on the gross-out factor of using a thermometer in, shall we say, different orifices. One goes in your mouth, the other... well, let's just say you probably don't wanna mix 'em up, unless you're into that kinda thing, which, judging by your taste in jokes, you might be. Here's a fact: You probably still think farts are funny, don't you?