One of my favorite ironic moments of the play is Romeo's tragic lines about hot alive Juliet looks before he drinks the poison to kill himself because he thinks she is dead.
She is just about to wake from her fake-death, and Romeo spends 30 lines or so in Act V, scene iii to tell her seemingly dead body how alive it actually looks. He notices the color coming back to her cheeks, the warmth of her body, and the beauty that has not been altered by Death's presence.
So he kisses her alive body and takes the poison to kill himself.
NOT THIRTY SECONDS LATER, Juliet wakes up wondering where Romeo is. Boy, that really stinks.
The greatest irony though is the fact that the hate between these two families was destroyed by true love.