Rumer Willis is a very charitable girlfriend when it comes to her steady guy, Jayson Blair, Breaking Celebrity News is exclusively reporting.

At a fundraiser for Direct Relief , Demi Moore and Bruce Willis' oldest daughter offered up a date with her The New Normal star boyfriend as a live auction item!

"It was totally spontaneous," a guest tells us.

The winner wasn't one of the attractive women at the bash, but an acclaimed chef.  Frank Ostini, owner of the Hitching Post II restaurant in Santa Barbara's Santa Ynez Valley -- made famous as the setting for the movie Sideways  -- bought the "date" and has invited Rumer to come al