Simply put, dramatic irony is when a person makes a harmless remark, and someone else who hears it knows something that makes the remark have a different, and usually unpleasant, meaning. For instance, if you were in a restaurant and said out loud, "I can't wait to eat the veal marsala I ordered," and there were people around who knew that the veal marsala was poisoned and that you would die as soon as you took a bite, your situation would be one of dramatic irony.
Lemony Snicket, The Reptile Room
humor, irony