big deal

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Something of great importance or consequence.
• noun An important person.
• interjection Used ironically to indicate that something is unimportant or unimpressive.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic Something very important, difficult, or of concern.
• interjection idiomatic, sarcastic Indicates that something is not important or impressive; so what.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an important influential person
• noun anything of great importance or consequence