I was doing the Pixie quest for spawning a mob the other day, and I started fighting it, some rando showed up and started attacking it, so I stopped and let them do it. Then my quest was finished and theirs wasn't, so they had to spawn theirs and do it again. Serves them right. I didn't need help.
You must be a real blast at parties.

I guarantee you that the other person didn't care. If they did, they wouldn't have helped. Keep on "punishing" people for trying to be nice or whatever, though.