I've been on both ends of the scale - instigator and victim. Overall, I like to make characters that are interesting, fun and at least a little unusual, but at the same time aren't dead weight. And it does annoy me when someone puts together a character that gets played in a way that is heading in the direction it'll get mine killed as well.
Sometimes I can't help saying something, but I try to watch my mouth. After all, it's not my character and as long as they are having fun and it's not at my expense, I try to let them roll with it. If I do offer advice, I always try and word it as "You know you could..." instead of making it an order; if they don't take my advice, well, that's their choice. Some people though, can really push my buttons - there's two in my group right now that really grind my teeth sometimes and make me headdesk often, and I just have to grin and bear it.