How about the "it's my vacation and I'm going to do whatever I darn well please" crowd? It all comes down to respect and manners. I do my best to ignore them.
As far as forum posts -- I wouldn't call it a real pet peeve, but occasionally we get a poster who asks for advice right before leaving for a cruise that might not be right for them, or who are cutting it close with the timing of air schedules, or didn't purchase insurance. I feel badly for them, and wish they had gotten more advice up-front. I wish we (meaning all of us) could help more in cases such as this.