How ironic that the things we say and who we are outside is so different from who we are inside.
How I learnt the word:
friend:"....you? fat chance."
me: "oohh cool.. :)"
friend:"no dumbo, fat chance = slim chance"
friend: now you know whats irony...
Its how when someone asks you: how are you?
and you answer with a smiley face "I'm fine, thank you!"
...When you're just dying inside