Someone who consistently makes comments that cross the line. Someone who doesn't understandwitty banter, instead moving to insults. Typically a meathead, or someone who lacks the intelligence to burn someone in a humorous manor...
An insulting term for a white person who dislikes people of other races. This is a reference to the Ku Klux Klan, which burns crosses in ceremonies celebrating their racial beliefs.
Some one who is known for crossing lines consistently without caring. Can include telling people off, saying things you should not around other people, doing things to other people/other people's property.
A line-crosser can be someone who upper decks someone's toilet or putting an air horn in someones ear.