You see, in the realm of real-life inter-person communication, trailing off signals a certain set of things. The recipient then scans through this set, and compares it to the possible set of additional meaning that could be attached to the words preceding. In this case, the poster is 'cutting-out' as they would be in response to the communication recipient making some sort of micro-gesture upon realization of the incongruity of the sent communication, in order to allow them to be sure that it was, in fact, a joke/sarcastic/irony.