Let us remember Act II scene 4, which basically features a war of words between Mercutio and Romeo, with Mercutio using a series of highly elaborate and funny puns to show his wit. He is a jester-type of character, who always appears to have a smile and a laugh for whatever situation faces him. Even in his death scene right up to his final plague on both of the houses, whose feud has led to his death, he continues his tendency to pun and to laugh ironically about his own situation. Note what he says:
Ask for me tomorrow, and you shall find me a grave man. I am peppered, I warrant, for this world.
Note the play on the word "grave," refering both to the situation of his health, that is serious, but also the fact that he predicts he will be in his grave tomorrow. Likewise, the phrase "peppered" refers to having been given a deadly wound, but also peppered food that is ready to eat, just as Mercutio is ready to die.