What is an example of irony in Act 2, Scene 1 of Romeo and Juliet?

Okay, Act II, scene i - I suppose it is ironic that Mercutio and the boys are trying to find Romeo and yelling for him the name "Rosaline" to get his attention, when now Rosaline has no meaning for Romeo - he has become enamored of Juliet and has spent the time wooing her during the famous balcony scene.

What's an example of situational irony in Act 2, Scene 1 of Romeo and Juliet?

In this scene, Mercutio and Benvolio have witnessed Romeo climb the wall surrounding the Capulet property and jump into their garden. They desperately wish him to be with them and cry out to him, to no avail; Romeo is deaf to their call, for he has only one purpose in mind - to be with Juliet.

Mercutio, in order to see Romeo, mentions that he will use magic to at least see or hear his friend utter even a sigh. He beseeches Romeo to say but one loving word, so that he may know that he is unharmed. However, his appeal goes unanswered. He realises that Romeo is not going to respond to his call and that he must "conjure" him, making references to Rosaline. Because of this, Romeo would appear to them.

Benvolio comments that if Mercutio should use Rosaline's name in such a way, Romeo would be upset, but Mercutio says that he only wishes to "raise" Romeo, i.e. awaken him, make him respond to their call, and therefore it is fair that he should so 'abuse' Rosaline's name.

The situational irony lies in the fact that Benvolio and Mercutio are under the impression that Romeo is in love with Rosaline and all their remarks revolve around her. Mercutio's lewd sexual references have Rosaline as the subject. The two are completely unaware of the fact that Romeo has now fallen head-over-heels in love with Juliet and any references to Rosaline would have no effect on him at this point.

Furthermore, they are next to the Capulets' wall yet they speak about Rosaline, when in actuality, they should be making references to Juliet. However, they do not know of Romeo's new romantic interest.

What's an example of situational irony in Act 2, Scene 1 of Romeo and Juliet?

In Act II, scene i, Mercutio and Benvolio see Romeo sneak off behind the Capulet house.  Romeo initially came to the party because he wanted to see his one true love (Rosaline), and he ended up meeting his newest love, Juliet.  Mercutio believes that Romeo is sneaking behind the Capulet house to be with Rosaline, and he calls bawdy jokes to Romeo.  It is ironic that Romeo is looking for his "one true love", but it's not who Mercutio thinks.  Mercutio tries to "conjure" Romeo up by calling out Rosaline's name, but he no longer cares for her since seeing Juliet.