It would be ironic for a firehouse to burn down. It would be ironic if an accountant was not good at balancing their check book. It would be sarcastic if one calls an ant a "huge animal". If someone was very strongly offended then replied "thank you very much"... this is being sarcastic. Sarcasm is often seen as being rude if used during arguements, though it can be seen as funny when used in a playful / happy way. Idealistic is tough to describe, though it might mean when people act due to their principles. If a person has an opinion of how things should be (ideally) and then act based on that, they are being idealistic. Chances are if I did a good job explaining these words then you now have a better understanding of them. ("chances are.." is used to say that something is probable or likely to occur)

I can say someone is idealistic when he is trying to achieve this high perfect standards in his life, person has its ideal or ideals, his principles which are of high morality and person wants to realize them in his life. I am sarcastic when I try to make fun of someone in order to show something. I can say you are sarcastic when you are telling me things that annoy me or others, when you speak with sarcasm Ironic situation is an amusing one, or an article written with irony, where journalist tries to show to the public particular situation in an amusing way and sometimes there is also sarcasm.

idealistic. - having a strong believe in perfect standards and trying to achieve them, even when it is not very likely sarcastic - person showing their unpleasant attitude to sb/sth often in order to make fun of it ironic - something strange or amusing, different from what you expect.