What are some of the most poisonous mindsets you would like to make newbies aware of?

For me, I would say that "I'm a nice guy" is the worst mind set in this community. This basically says you're self-centered and deserving of some type of royal treatment. In a sense, it also says you don't need to work on improving yourself anymore. This is the all-in-one package that gives the person and everyone else around them a bad name.

Many of us know this one, but I'd like to know your worst poisonous mind set.