Quite often sarcasm is mistaken for irony; however, sarcasm is a form of irony which uses sharp wit to highlight the obviousness, stupidity, or annoyance-factor of a situation. One main difference between irony and sarcasm is that irony is generally observed and sarcasm is generally created (i.e. spoken, written). People don't usually go about actively pursuing the creation of irony. 

Oxford English Dictionary definition of Sarcasm: "If I could say this and roll my eyes it would be funny."

Sarcasm is the "use" of "quotation marks" around any "word" to "make" it "funnier". 

A good example of sarcasm: "I appreciate your help", when no help was provided to the speaker. My English husband is a pro at this kind of humour. We can also observe that this kind of humour isn’t the ‘funny ha-ha’ kind of humour but rather more a wry kind of humour and not always funny for the party at the receiving end of the comment.