I can be extremely boring in boring company. I'll hate every minute of it, but usually don't seem to be able to be entertaining, funny and interesting without a playmate. Something about needing input in order to create humor and knowing that if my joke doesn't go all the way, the playmate will carry it to it's hillarious destination (or if he/she fails, I've gotten the extra second or two to think and can now pick it up again and take it in a new silly direction.)
I guess it's because I'm introverted and don't want or am able to carry an entire talk show myself.
That said, I'm rather good at creating plamates out of people who normally seem to prefer to be boring, but who have a silly side deep in them. Even some SJs can be made funny playmates if I just nudge them the right way (but it normally takes too much energy for me to try it unless I'm desperate.)
Edit: Ah, but in general on internet forums, I normally find NTs much funnier and less boring than NFs. That said, it's more about individuals than about type. 2/3 of the NTs on INTPc are extremely boring (sure they have potential, but don't use it), while
prolsnon's like Ivy forces all kinds of beverages out through my nose. And people like Kuranes and Jen could never be boring even if they didn't make a single joke, so it's not just about humor.