It is a common way to hype up a word. Would you be offended if someone types, "GOOOOOOOOOOOOOOOAL" since it is a prolongation which is also a type of stutter? In everyday life I hear words done like this. One needs to think of the INTENT of the post. Is he REALLY mocking a person who stutters? Is he posting it AS A STUTTER? I would say no to both of those questions.