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Brackets that represent an unfilled tick-box. Hence the writer is asserting that the statement following the brackets is untrue. Often used for humorous effect, and to contradict or point out an error in what someone has just said. Somewhat similar in meaning to adding "NOT" after a statement. Multiple tick-boxes are often strung together, like a check-list of true and false statements. { } is the opposite of {x}, a checked tick-box which means the statement is true. (Note - curly brackets are used in the examples, since urbandictionary uses square brackets to denote links. However in real usage, square brackets should always be used.)