Well, here is what happened in my college calculus final exam last year.
I had me a few tacos the night before and something did not agree with me (my guess, bad sour cream).  I had developed ?the trots? less than 20 minutes before class started.  I had a C in this class and this grade would push me into A territory if I could finish it.  Walked in and started taking it, intestines bubbling.  I held nothing back and farted as much as possible (small trickles of crap came with it).  The putrid smell overcame many people around me as I heard them inch their desks away from mine.  I could barely stand my own stench for the next half hour.  I could not think because of the pain, so I asked the prof. to excuse me to the restroom.  He allowed me to go, as he could smell my condition.  I exploded in the restroom and the splash force from the toilet left a nice ring of sh!t where the water does not flow in the bowl.  I am sure the janitor had a field day.  I was running short of time and I was not going to finish my test, so I shoved toilet tissue into my ass crack to absorb any moisture as I did not have time to fully wipe.  I returned to class as smelly as ever and sat back down.  A few people had switched desks while I was out.  I was momentarily relieved after my last bowl movement, but it only lasted for a short time.  The farts started again, as did the "sharting".  The smell remained terrible as people around me turned in their tests way too early.  I was forced to return to the restroom and repeated the same thing above.  Finally, I returned to the class and finished the test.  Turned it in, but I missed a good deal as I was not able to concentrate.  Ended up with a B in that class and a whole list of enemies (or at least people who shunned me).