This question is going to be difficult to answer definitively, because the way in which Mercutio is going to deliver this speech will be different in every production. I remember in particular the way in which Mercutio delivers this speech in the Baz Luhrman production of the play, starring Claire Danes and Leonardo DiCaprio, when he beings to speak the lines in a playful manner, but ends up being overwhelmed by the emotion of anger in what he is saying and needs to be calmed down and reassured by Romeo when he is told that he "talk'st of nothing." Anger is certainly an emotion that could easily be expressed as Mercutio presents a much more bawdy vision of life than the gentle romance of the play suggests.
Equally, however, a director could easily choose to let this speech reflect Mercutio's more light-hearted and humorous nature. The deliberate move towards crude language is something that is shown towards the end of the speech and is something that Romeo is so shocked or embarrassed by that he feels the need to interrupt it:
This is the hag, when maids lie on their backs,
That presses them and learns them first to bear,
Making them women of good carriage.
This is she--
It is at this point that Romeo tells Mercutio to stop his ramblings, perhaps because the vision of love and romance that Mercutio offers is so discordant with his own lovesick feelings.