The worst insult I have had is when a pax turned up after the flight had closed and pushed back and I was closing up for the night. I explained that the flight had pushed back so I couldn't get him on it as it was no longer at the gate. I got called a f
g c
t and other variations on a theme. You should have seen him run though when I picked up the phone to call the police.
To be honest, you get so used to name calling and insults that it becomes water off a ducks back. I find we get more insults now that we have stricter baggage rules that we have to enforce.