Irony is poison. There is nothing in written English as destructive to the writer’s effectiveness.
Irony requires snark in the voice and few, if any writers, can adequately convey that tone, especially in a headline, to wit, today’s:
100+ Valedictorians swarm railroad cars in Chicago — Stealing everything in sight
Valedictorians? Of course not. Thieves! Does the writer disrespect genuine valedictorians?
The reader can not possibly know why a mass of overachieving students could gather in one place to steal railroad cars (that is what it says!). Many people will not get the snark because they simply do not read at a level of literacy that enables them to pick up the childish snark that unlocks the real purpose of the headline: condemnation.
The more accurate and persuasive headline would be straightforward:
100 Chicago Train Yard Thieves Pillage Rail Cars
Avoid irony! It is a deadly plague that kills a writer's best ideas.
Now, here are a few pretty eggs to look at. Aren't they lovely? There is no irony here. They are perfect just as they are.
Yes, most people will say that example of sarcasm or hypocrisy is "irony", but irony is a rarer element. Isn't it ironic?