Although the Celebrity was almost impervious to sarcasm, he was now beginning to exhibit visible signs of uneasiness, the consciousness dawning upon him that his eccentricity was not receiving the ovation it merited.
Because sarcasm and irony often go together, people often use sarcasm to refer to irony. Strictly speaking, an ironic statement is one that means the opposite of its content, and a sarcastic statement is an acerbic or sardonic one. To distinguish the two, saying "Oh my god, I hate you!" to sincerely congratulate one's best friend on their good fortune is ironic, but not sarcastic; saying, "I'm not a mind reader, okay?" is sarcastic, but not ironic.