ok, this one's kinda bad, but i love it.
A group of medical school students enter the morgue for their first course in forensic pathology. The chief medical examiner is standing before them with a corpse laid out on the autopsy table. as he pulls back the sheet, he tells the students
"There are only 2 things to learn about being a good pathologist. 1) don't be disgusted by a dead body."
as he says this, he takes his glove off, inserts a finger in the body's behind, and sticks it in his mouth. he asks each and every student to repeat what he did. horrified, they do.
" #2 students...pay attention to details! i stuck my first finger in the corpse, but put my middle finger in my mouth."