Legendary comedian David Brenner has died at the age of 78 ... and he went out with a joke. Brenner's rep says David passed away peacefully Saturday evening at his NYC home surrounded by family. As we previously reported ... Brenner slipped into a coma this week after his cancer got aggressive and…

David Brenner -- who holds the record for number of appearances on the "Tonight Show" with Johnny Carson -- is on his death bed and people close to him say it's just a matter of days. Sources close to Brenner say the 78-year-old comedian has cancer that has been aggressive ... spreading rapidly.…