Question
Are there more than one possible reply to the insults? I vaguely remember playing Secret of Monkey Island a long time ago and ending up in a sword fight against either a pirate or the sword master, unfortunately can't remember which one. They threw an insult at me which I didn't have the correct counter-insult for yet, so I replied with another one that was kind-of fitting. And won the match despite using an "incorrect" reply.
EDIT: I'm not sure if the insult was this one, but this is what I mean:
Insult: Only once have I met such a coward!
Reply: He must have taught you everything you know.
Alternative reply: I'm glad to hear you attended your family reunion.
I don't currently own a playable version of Monkey Island so I can't verify if they work myself.
Answer
Yes, some of the Sword Master's insults have multiple valid comebacks. I just tested these on the Special Edition, but they should work in the original game as well.
Insult: Only once have I met such a coward!
Comeback #1: He must have taught you everything you know.
Comeback #2: I'm glad to hear you attended your family reunion.Insult: I usually see people like you passed-out on tavern floors.
Comeback #1: I'm glad to hear you attended your family reunion.
Comeback #2: Even BEFORE they smell your breath?Insult: My name is feared in every dirty corner of this island!
Comeback #1: So you got that job as janitor, after all.
Comeback #2: Too bad no one's ever heard of YOU at all.Insult: My last fight ended with my hands covered with blood.
Comeback #1: I hope now you've learned to stop picking your nose.
Comeback #2: Your hemorrhoids are flaring up again, eh?
There might be more, but those are the ones I could find. I don't think any of the "regular" insults have multiple comebacks, though.
Check more discussion of this question.