200% with you, Giok, especially the first paragraph - it's a gem.

But I would never walk out if someone sang a parody of song I just did - even if the parody was bad, even if the song was mine. That's being a bit "precious" by my reckoning.

As for the last category you mention - I know someone like that, though I believe in his case there are feelings of inadequacy involved too (he doesn't believe he can produce a good original, but I think he underrates himself). And there is the need to make others laugh, as a defense mechanism - a little like the jokesters at school. It's true, he doesn't have a great voice, and I suspect he resorts to humour because of that. Shame, because I think he is a perceptive person, and with a little effort he could surprise himself and others.