Ouch. Don't insult the other guy...

Taking a jab at "the other guy" that is, the person you think you are competeing with just makes you look desperate & jealous as the underdog. Clearly you wish you were in the position they are in. Taking a shot at the little guy makes you look like a bully.

It really is true that if you don't have anything good to say (except maybe if you have earned the right to tell the truth vis constructive criticism directly to the person) you ought not say anything at all.

But then what about the PC/Mac commercials? I actually stop the DVR to watch them.