being ironic is not just being sarcastic, being sarcastic is just making a cutting remark, being ironic is saying the oposite of what is meant, say you had an argumant with a girl and said something bad and she ran out of the room, being sarcastic i would say something like
"that wasnt a good thing to say was it"
but if i was being ironic i would say something like
"well you've certainly made her happy"
i did my examples above so read them