Watching an episode of Scrubs the other day, I was reminded on an incident early on in the academic year when I was an intern.
A classmate of mine was asked to perform a digital rectal exam on a patient with lower GI bleeding. While we were out in the hallway on rounds, and he was doing the deed, we heard an Oww!!! coming loudly from the patient room.

Now rectal exams ain't fun; I've been on the receiving end before. But it shouldn't really hurt, instead causing a weird need-to-poop sensation.

Unless you use the wrong lube.

Yup. Poor guy (the patient, but the intern too, as it was traumatic for the both of them I'm sure). The intern had mistook the alcohol disinfectant for good-ole KY lubricant. To add salt to the injury, quite literally, the source of the hematochezia was apparently a small anal fissure which didn't receive the alcohol too well.