<human>: Can you provide a brief rundown of the text in within 3 sentences?

I will preface this story by saying that I have irritable bowel syndrome and have had many photo finish moments.  That said, the worst experience happened while I was on a boat cruising down the river.  My friends and I had been boating for about a half hour and we had just arrived at our destination a little ways up a smaller connecting stream where there was a rope swing and multiple rocks to climb and jump off.  I had started to feel something was not right in my stomach but after years of IBS I usually dismissed this feeling and on most occasions this worked fine.  I soon realized that this was no ordinary shit coming on and I required immediate bowel evacuation.  I begged my friends to turn and go back downstream to find a bathroom but they all just kind of told me to suck  it up since we had just got to the rope swing.  At this point I am having stomach convulsions and holding back the monumental poop coming on had caused sweat to poor from my body.  I shove my friends out of the way as I fill a water proof pretzel container with wads of napkins and a few of the brown paper bags we brought our lunches in.  I then dove off the boat swam to the nearest rock and unleashed one of the largest poops I have ever taken.  My friends did not miss this opportunity to take pictures and ridicule me for years after this event.  In retrospect I wish I would have just shit while swimming but at the time that grossed me out too much and the rock seemed to be my best option.
<bot>: I frequently have the urgent need to poop.  The call came while on a boat in a river.  I shit on a rock as my friends pointed and laughed.