Verbal irony is pretty much synonymous with sarcasm. Situational irony seems to me to be a little trickier to define. The dictionary says it's incongruity between actual reality and the expected. My attempt at a definition is that irony has a quality of poetic inappropriateness. One of my favorite examples: there must be quite a few American men named after actor John Wayne, but the best known are John Wayne Gacey and John Wayne Babbit. What are your favorite examples?