When you get someone in a sibgaround or whatever who insists on saying how terrible they are - not in a jokey way, which is fine, but in a hyperapologetic way - and the going on to do something perfectly well, I admit to finding it annoying, even a bit insulting. What they are actually saying in a way is "if you think I sound ok, you are lacking in taste - and all these other people in the room who you think who sound no better than I do are rubbish too.

Being modest doesn't mean running yourself down, it means doing the best you can, and listening to any criticisms with respect and equanimity. (Ah, I wish I could always do that, especially when some ignorant bastard doesn't appreciate how brilliant I really am...)

As I said, I'm not talking about joking, like saying "Well, you've asked for it, on your ears be it..." or something like that, when you get invited to play or sing. It's a bit of a cliche, but it's better than coming on with an attitude "Now listen to this, this is how it really should be done" - even if you really are that good.