Beatrice is a headstrong woman, who speaks her mind. I get the impression she has been hurt in the past by Benedict, and now will not allow any man, let alone Benedict into her heart for fear of being hurt again. Instead, any man brave enough to show an interest in her is ridiculed. Benedict has a similar defence mechanism. As a soldier and a confirmed bachelor, he enjoys the company of his comrades and swears he will never marry. He is sure anyone who does must be weak. I think he feels anxious about lowering his guard with Beatrice, and letting her see his softer more vulnerable side, opening himself to possible derision. .
Beatrice's feelings towards Benedict are made clear from the very start when she asks of the messenger, "I pray you, is Signor Mountanto returned from the wars or no". The sarcasm in her words gives the reader the impression that something has happened in the past and that maybe there is unfinished business between the pair of them. This is confirmed shortly after, when she says, "He set up his bills here in Messina and challenged cupid at the flight". Their volatile relationship is put into more perspective when Leonato tells the messenger not to worry, as there is a merry war between the two, and whenever they meet, there is a skirmish of wit. When they meet for the first time in the play, immediately they try to outdo one another, with put-downs, each trying to have the last word.
I believe that Shakespeare presents the couple as being rather insecure. There is an attraction between them that is confirmed later in the play. They are both afraid of rejection from the other, preferring to scorn one another, rather than admit their true feelings. It takes a plot from their friends to get them to admit to themselves and everyone else that they do indeed love one another. In Benedict's case, Leonato, Don Pedro, and Claudio use Benedict's ego and machismo to their advantage.
