Do you think good-natured teasing often goes too far? Have you ever gotten seriously offended by a joke that crossed the line? Have you been informed that your own teasing hurt someone else's feelings?
Yes, yes, and yes.
I think most teasing is not good-natured, as it seeks to elevate the teaser at the victim's expense. In of itself, this is problematic as it allows groupthink and labels to define people rather than the people themselves. Teasing is just ad hominem, an attack against the person. More often than not, teasing is an excuse for certain people who are more popular to crush any opposing viewpoints. Since certain people think teasing is "funny" then it permits discrimination as long as there is clever humor.
That being said, I have crossed the line at times, and I admit I have been wrong. The problem is there is unwritten protocol as to what teasing is allowed and what is not. I am of the belief that either everything will be allowed and no one censors another, or that none of it be allowed. If what offends you is crossing the line, then what offends me is crossing the line as well. To do otherwise is hypocritical, which is why it's best not to allow teasing and potshots at all. It's always one-sided.