Most discomfort I ever felt was when I had to have an endoscope put down my nose. They didn't tell me I had to inhale the local anaesthetic so I felt the endoscope scraping against the back of my mouth and throat. I've sniffed the spray every time since!
Some mild discomfort but I managed to grin and bear it. There was a nasty aftertaste and numbness for half an hour afterwards too.