In the early acts of the play, both Beatrice and Benedick can be described as two characters who love to hate each other. Both characters are very similar and it is their similarities that make them want to hate each other.
One similarity is that both Beatrice and Benedick love to make witty jokes. In fact, both characters constantly try to outwit each other. We especially learn this when we see Leonato tell the messenger reporting the prince's safe return from the war not to misunderstand Beatrice as, even though Benedick is acknowledged to be an admirable man, Beatrice loves to insult him because they love matching wits, as we see in Leonato's lines:
You must not, my lord, mistake my niece. There is a kind of merry war betwixt Signor Benedick and her. They never meet but there's a skirmish of wit between them. (I.i.50-53)
However, one difference between the two characters is that Benedick likes to back away from a fight while Beatrice likes to pursue fights. We especially see Benedick back away from Beatrice's battle of wits when we see him say that he wishes his horse were as fast as Beatrice's tongue, meaning that Beatrice responds with remarks faster than Benedick's horse runs. We then see him proclaim that he is done fighting with her, as we see in the lines, "I would my horse had the speed of your tongue ... I have done" (I.i.120-122).
Another similarity between the two characters is that both proclaim that they love no one and will never love anyone. We see Benedick proclaim that he loves no one when he states that all women adore him, except for Beatrice, and that he wishes he could return their affections but instead loves no one, as we see in his lines:
But it is certain I am loved of all ladies, only you excepted; and I would I could find in my heart that I had not a hard heart, for truly I love none. (I.i.105-106)
Beatrice responds by saying that is a great relief for all women as they could not trust him and then states that she also does not love anyone, as we see in her lines, "I had rather hear my dog bark at a crow than a man swear he loves me" (I.i.110-111).
Hence, we see that both characters love to hate each other, which lays the groundwork for their upcoming union in the play.