As a fellow Luffy fan, I definitely think you're in the right. If someone has a cocky mouth and keeps mass tagging and mocking you throughout those last months but runs away the moment his theories don't come out to be true, he shouldn't expect that users like you welcome him with open arms. It's just a cowardly act, that's it.
Some Zoro fans did the same and people mocked them for that. Heck, I remember a certain user temporarily leaving the forum and people kept writing insults to his profile until his return but prior to that, this user also provoked others like that.
So what's the message at the end of the day? Don't dish out what you can't take. This also includes for Pringles.
Plus, there is always the ignore button if it bothers him that much.
I still have users like MoNSteR(whatever) on ignore as well.