Most trolls believe that they are, in fact, funny. Anyone who does not agree with them is obviously either: overly sensitive, has no life, no sense of humor, or is a combination of two or all of these. In many instances, one can see where troll has in fact messed up but is too wrapped in his own little laugh to notice how much of a fool they have really been. These trolls are the easiest to identify, as they often stop leaving comments when it is obvious even to a monkey with a brain tumor that they have fudged it up, or when you see a comment that begins with telling the owner of the site/picture/story/etc that they suck for no good reason. To be absolutely sure, look for the word "lulz" anywhere in their comments, or YHBT at the end of the comments.