I find abusive comments and just write "Abusive comment" in my report as there is no more explanation to give but when I find something not making sense, I don't get what explanation to give and just write "an off topic/spam post". May be I should now give detailed reports as few of my reports have been already marked bad.
Usually that would be enough, but you have to remember what is spam or an 'abusive comment' or post that doesn't make sense to you might make sense or be completely valid to others.