I think I can actually handle 'good' input/criticism. I think it's how you deliver your comments. "The voice kinda suck", "I can't tell what it is, but the song doesn't sound good" would be a couple of the unacceptable ones.

Although I will have to say- sometimes it depends on who gives the comments too though. I know somebody who pretty much gave me numerous 'suggestions' while she couldn't even get her stuff right. Couldn't even get her syncopation down, but kept correcting everybody else throughout our band practice, to me that's pretty frustrating.