"Much Ado About Nothing" is humorous and playful in tone due to its extensive wordplay and witty dialogue. In particular, the play is irreverent in its discussion of sexuality despite the taboo nature of this subject in the characters' social circle.
This is evident in the characters' use of sexual innuendo. For instance, when a messenger describes Benedick in Act 1, Scene 1 as "stuffed with all honorable virtues," Beatrice puns on the notion of "stuffing": "He is no less than a stuffed man, but for the stuffing—well, we are all mortal". Here, rather than condemning Beatrice's deliberate sexual pun, the play presents it as evidence of her quick wit. When Margaret's sexual innuendos elicit protest from Hero and Beatrice in Act 3, Scene 4, the play appears to take Margaret's side in affirming that there is nothing wrong with talking about sex, thus cementing the irreverent overall tone.
However, the play only sanctions frank discussions of sexuality up to a point: the tone darkens significantly when Hero is wrongly accused of having an affair and condemned by both Claudio and Leonato. Only "legitimate" forms of sexuality—or, as Margaret puts it, sex between "the right husband and the right wife"—has the play's outright approval.