The mystery robber made off with the cake after crashing the Los Angeles party on Tuesday night (15Feb11) - and then boasted about it online.
The man, calling himself Paz, posted a note on his Facebook.com page, which read, "I crashed Paris Hilton's Birthday Party and Accidentally the Whole Cake. I woke up this morning with a birthday cake in my living room. It's big. It's red. It says 'Paris'. And it's f***ing delicious."
He went on to reveal a pal named Kevin had sneaked him into the party and, after "drinking heavily" he made off with the cake after Hilton blew out the candles.
Paz ends his post by revealing, "I don't know WTF (what the f**k) I'm going to do with it."
Paris Hilton herself has yet to confirm Paz's story.