I think that writing or reading a blog sometimes does not portray the feelings. So I try to take everything into perspective. I've been offended by explicit sexual content, just don't feel it's appropriate on a blog.
It's pretty hard to offend me, though an acquaintance who's a prolific email forwarder almost to the point of spam did exactly that last night with a racist joke. I asked her to keep that garbage out of my inbox.
By and large, racism, bigotry and intolerance in any form are what get me going. And convince me to quit reading. So do personal attacks, insults and general bullying. I don't even bother to respond to those -- wouldn't want to give the writer the extra page view. ;)
I'm not offended by ideas, though. I'm fairly liberal, but I will -- and do -- continue to read blogs with conservative slants if they're well-written and not nasty. We can all learn from each other.
Sure - but I have offended others to. Basically I think you have a right to your opinion and to state it as you please, but I also have the right to disagree and to state that. I will respect your right to decide what you believe as long as you respect my right to say I disagree. What bothers me is bloggers who have no problem voicing their own views but then get very upset if you voice your own and don't agree with them. Those types of blogs I don't go back to. But if it's an author that is willing to engage in an adult discussion with the readers, that's awesome