Disrespect – Respect given is respect earned. Naturally.
Ignorance – “I can hear you and I know you are talking to me but I choose not to acknowledge you! You do not exist to me! Lalalalalala!” (being interrupted by random people during play, aftercare or when talking also come under this category)
Lousy liars – If you are going to lie, at least lie properly.
Thieves – Simple. If it is not yours, be it an idea, a photo, something material or even credit for an achievement or action: THEN IT IS NOT YOURS!
Cattle – “Follow! Follow! We know not what we are following! Wheeee!”
Being called a vampire – I am not a vampire! (see #1 and #2)
Drugs – A lousy excuse for having no imagination. Incredibly stupid when mixed with BDSM (overconsumption of alcohol being the most common I have seen).
Knowledgelessness (BDSM) – If you are going to be brutal, at least do the decent thing and get creative with it or do something that actually requires some element of knowledge and skill (this would also imply actually having the said knowledge and skill for the use of any tools involved, rather than just grabbing something and hoping that nothing is permanently damaged during its application). Get some learning. Take time to plan. Be consensual and safe. DO THE RESEARCH!
Trolls – Sad, pathetic and pitiable people who literally have nothing better or constructive to do than slander, criticise and argue online. “Get a life”.
The fact that I frequently hear and see all of the aforementioned far more than I care to.