"Sarcastic " is an adjective. It describes a person or a saying (sentence or word or utterance). It means ironic, intending to pain, ridiculing, or saying opposite to what a person is expecting, often on the face of the person.
Example: (a conversation)
Bong: "Hi friend, look that picture is so beautiful !"
Bing: (not so impressed by that) "yeah, Just like your face! "
Comment & usage: Here Bing made a sarcastic remark on what Bong said.
Bong: "Hi friend, let us go quickly, the others may be waiting for us."
Bing: "Hey, are you the President of India or what for them to wait for you?"