Too many to list. Most not suitable for this forum. One of the worst...
I was FO departing EWR after a layover. Something I ate the night before was grumbling and tumbling in my guts. The first gentle whispers of distress began during the start checklist. No problem, I'm thinking, I'm good for at least a couple hours yet. During engine start, I'm beginning to develop those strong "Gotta Go" crampy gripes.
As we taxi out (full AC), I reach a certain point of suffering. We've all been there. If I don't offload in the next 2 minutes, it's going to be an epic, vile disaster. I'm pale, and big beads of sweat are forming on my face.
"STOP the JET NOW, I'VE GOT TO HIT THE LAV, FAST!!!"
The captain is laughing his a$$ off as I leap out of the cockpit and fly into the lav. All of first class, and the FA's, are staring directly at my doubled-over, staggering form as I burst through the CP door. Are we on fire? Is there a terrorist? Is the Captain dead?
Now the worst happens, as if it's not already pretty bad. This is graphic. Don't read it if potty humour offends.
Keep in mind, all of this is unfolding on the parallel taxiway at EWR, with traffic backing up behind us, and ground asking if we need help.
OK. You've been warned.
At high pressure, the vile remains of last night are audibly ejected in the 1C lav toilet. Worse than the noise is the stench. One of those "once every 5 years" bit of toilet pollution that carries on the breeze like a squirt of VX nerve agent. The cabin is polluted to a degree that defies description, with the entire aircraft load staring at the unfolding drama in total, amazed silence. To this day, I cannot describe the utter, ultimate humiliation as I scooted back forward to my FO seat. It still makes me cringe.