Also, please note that LB is one of the nicest posters in the CR. She is definitely NOT someone you have to stay away from.
As for posters not to start up with, as LB wrote, it would be Loshon Hara. Also sometimes, it’s a matter of “getting” people and figuring out how to relate to and react to the particular poster. You kind of figure it out with time.
When I first joined the CR about a year ago, a very wise poster named Little Froggie pointed out that I should have lurked for a while before posting. After being here a year, I see his point.