Why wasn’t D.C. Mayor Vincent Gray at the State of the Union address Tuesday night?

Awww, did no one invite him? Nope — Gray blew it off to attend a party for his girlfriend, Linda Mercado Greene, who celebrated her birthday that night.

The mayor’s official schedule was blank that night. His office said Gray was invited to the speech as a guest of D.C. Del. Eleanor Holmes Norton, but he declined so he could attend a “family function.”

Turns out he was at Cafe Milano, where about 40 people gathered in the private room upstairs to celebrate with Greene, whom Gray has been dating for the past couple of years. The mayor breezed past customers in the restaurant — unlike council member Marion Barry (Greene’s former boss) and his son, Christopher, party guests who cheerfully worked the room.

One could argue, and plenty do, that Washington’s mayor should automatically receive an invitation to the president’s address out of respect to the federal city. Outspoken D.C. advocate Mark Plotkin tweeted his outrage Tuesday that Gray had not been invited by President Obama: “The ultimate ingrate. No invitation to Mayor Vincent Gray of DC to the SOTU. 93% in 2008, every precinct.”

Although Congress issues most of the invitations to the annual speech, the first lady invites a select number of guests who personalize the president’s key talking points. This year, Michelle Obama asked San Antonio Mayor Julian Castro, a proponent of solar technology, to sit in her box. (Mayor Kim Driscoll of Salem, Mass., attended as the guest of Rep. John Tierney.)

D.C. mayors rarely score an invite, which irks the heck out of statehood proponents who believe the District should be prominently represented at the high-profile event. And even when they do, it’s always something: Critics got mad at Anthony Williams when he accepted invitations to the event despite the lack of D.C. voting rights. Others took offense when Adrian Fenty snubbed Laura Bush and attended as a guest of then-Speaker Nancy Pelosi.

And Gray? No White House invite last year, so he went as a guest of Norton’s — but declined this time. (She brought Clayton Lawrence, founder of LEAP Foundation DC instead.)

A few other no-shows at the speech: Agriculture Secretary Tom Vilsack. Every year, one Cabinet member is tapped as the “designated survivor” in the event of a catastrophic attack on government officials in the Capitol. Vilsack, ninth in the chain of presidential succession, was spirited off to an undisclosed location (no details even after the fact, a department spokesman told us) for the duration of the speech.

Also not there: Supreme Court justices Antonin Scalia, Clarence Thomas and Samuel Alito (who created a flap by reacting to a presidential rebuke in 2010) because they don’t think much of justices attending what Chief Justice John Roberts called “a partisan pep rally.” Sonia Sotomayor, who was appointed by Obama, missed this year because she’s attending a judicial conference in Guam, according to news reports.

And Gray? The choice was love or politics — the lady or the tiger — and the mayor opted for his girlfriend. The couple has been out and about openly (they walked the red carpet together at the BET Honors this year and last) but didn’t advertise Tuesday’s birthday party.

But maybe he didn’t miss the SOTU entirely: Guests at the restaurant tell us the speech was broadcast both in the restaurant downstairs and on screens in the private party upstairs.