Tybalt is a stubborn, immature, and demeaning character, but he plays a very small role insofar as time spent on the stage. His actions, however, cause a series of events that gives the plot movement. It is my interpretation, that Shakespeare gives Tybalt characteristics that make him most disagreeable to the audience; therefore, when he is killed by the likeable Romeo, the audience is not deeply affected by the death (even though the rest of the play is affected).
Tybalt plays a minor role in "Romeo and Juliet" tragic love story on stage (he does not speak much lines than other characters), but then, he really influences the entire flow and progress of the entire story that makes his conspicuously small part in the play to a large and important factor in the story. Throughout this entire play, the audience could see his true character- angry, restless and obstinate behavior (especially to Romeo and his gang, even to his family), all due to long-lasting feud between the two families. He was later on killed by Romeo as an act of revenge as Tybalt killed his best friend, Mercutio, who provoked him, leading to a threatened sword-fight and bloodfest.
Why depict Tybalt with such devious and threatening words? I think the reason why Shakespere did this have a ulterior motive, to make sure that the audience watching his play would not sympathies with this horrible character and disagree with his entire actions. I think he is trying to make the play less chaotic and less complex and confusing.