I think most of the worst communication or the lack of communication occurs in the last Act. In fact, the breakdown of communication is so significant that it causes their deaths.
Friar Lawrence and Juliet had concocted a plan while Romeo was banished in Mantua for her to fake her death and for Romeo to come and rescue her. This planning occured in the end of Act IV. The Friar wrote a letter to Romeo so he would know what to do, but it never arrived! We learn this in Act V, scene i from Romeo's perspective, and in Act V, scene ii from the Friar's perspective.
By scene iii, Romeo freaked out and went to be with Juliet to kill himself because he truly believed she was dead. Balthazar heard the news of her death as real and reported it to him. Thus, I would look for Romeo's last lines in Act V, scene iii and look for evidence that demonstrates his belief that she is indeed dead. There is plenty.
The whole of the interaction between the Nurse and Juliet in Act II, scene v is a complete lack of communication. The Nurse has just returned from meeting with Romeo to find out when and where Romeo and Juliet will be married, and Juliet has been on pins and needles waiting for her return. In one of the (potentially) most comic scenes in the play, Juliet repeatedly tries to get information out of the Nurse, who repeated strays off topic, talking about her aches and pains, how fabulously handsome Romeo is, and even asking Juliet where her mother is.
Here's how the scene concludes, though I'm sure you could find any number of quotes to suit your purpose throughout the scene:
Where is thy mother?...How oddly thou repliest.
Are you so hot? Marry, come up, I trow.
Is this the poultice for my aching bones?
Henceforward do your messages yourself.
Come what says Romeo?
And then the Nurse, finally gives Juliet the information she has been craving, that they are to be married that day at Friar Laurence's cell.