Ignoring people is effective, but not necessarily fun. (It's a game, and all about FUN!)
Okay, so you did not choose the effective method and instead your character offered their character to a duel. Now of course some spammer at an event is not role playing, although I'm confident that they could come up with some back story about how they are indeed the most LEET RPER in UO, and whatnot, but that's neither here nor there.
So what to do? Well, accept the accepted duel, of course. Start a new character with 50 taming, if you have a slot available on that shard, otherwise my diabolical plan will not work. Oh, and use the same name for the character that you were on when you encountered said spammer-would-be-griefer.
Next, tease them along that your character is coming to the duel location in the fine land known as Felucca, but since that character is a resident of Trammel, it will take some time. (They are easily lost and very afraid of what might lurk in the shadows, yadda, yadda, yadda.) Accept defeat before you even begin! (But not to your opponent, of course.)
Then tame as many rabbits, or cats, or dogs, or rats, or whatever is possible, on the way to the d00ling site, newb.
Park the pets a short way from the site of your character's demise, ask them nicely to guard your character, and then proceed to the certain failure point. (Hopefully decked out in similar apparel that your real character was wearing.)
Of course, as SOON as the jerkie one has his (or her) character attack yours, RUN TO YOUR PET GUARDS!
Command the pets to kill and target your unworthy opponent, or whatever tamers use in battle these days to command their fine pets. (I have no idea. I'm retired from official UO. It might be better to name all your pets before hand with really ridiculously funny names, and have macros set up to command each to attack last target, and set last target upon immediate contact with the jerkie one.) But if the guarding command still works as I remember it, then I don't think attacking the aggressor will be necessary.
An added bonus goes TO YOU for using all birds. (Little ones that might be hard to target.)
Extra bonus points for screenshots for us to enjoy!
And, of course, try to keep your character alive long enough for the perp to go WTF!?! (or whatever strange language they speak these day) so that you can get your revenge and move on to better and bigger things. Now if you really, really want to have fun, have about 10 (or 20, or 30, or more) of your friends nearby on their own newbie tamers of very small birds, who are of course happy to come to your defense. Heck, I would even open a trial account to get in on such an adventure.