This is from prologue 1 line 5, and is ironic because the audience knows that the characters in love are gonna die, but the characters do not know.
"A pair of star-crossed lovers take their life"
"Whose misadventured piteous overthrows/Doth with their death bury their parents’ strife"
This is from prologue 1 lines 7-8, and is ironic because the audience knows that once the lovers die there will be peace between the two families, but the families have no idea.
"This holy shrine, the gentle fine is this:/My lips, two blushing pilgrims, ready stand/To smooth that rough touch with a tender kiss"
This is from Act 1, Scene 5, lines 92-94, and is ironic because the audience knows Romeo is falling in love with Juliet whose families are arch nemesis's, but Romeo and Juliet have no idea.
"Alack, there lies more peril in thine eye/Than twenty of their swords! Look thou but sweet,/ And I am proof against their enmity"
This is from Act 2, Scene 2, lines 71-73, and is ironic because many characters think that Romeo is still in love with Rosaline, but the audience knows that he has moved onto Juliet.
"God shield I should disturb devotion!/Juliet, on Thursday early will I rouse ye./Till then, adieu, and keep this holy kiss"
This is from Act 4, Scene 1, lines 41-43, and is when Paris is telling the Friar that him and Juliet will be married on Thursday, but the audience knows that will not be happening however, no one else does.
This is from Act 5, Scene 3, lines 92-96, and is ironic because we know that Juliet is not really dead.
"Death, that hath sucked the honey of thy breath,/Hath had no power yet upon thy beauty./Thou art not conquered. Beauty’s ensign yet/Is crimson in thy lips and in thy cheeks,/And death’s pale flag is not advanced there"