I will downvote, copy/paste, plagiarism, tag spam, and being offensive. I mean really offensive when it directed at another user or group of people. Not just the average run of the mill being a jerk.
I also leave constructive comments on articles that are borderline and headed in that direction.
I'm not downvoting as much as I'd like due to the fact that I like to upvote and support users too.
👍 - supported