In what could be one of the most talked-about Hollywood hookups yet, new pictures of Reese Witherspoon and Vince Vaughn have set off rumors that they're dating!

Reese and Vince were snapped in a passionate liplock in San Francisco yesterday. They were also spotted holding hands and looking mighty cozy in the frigid weather.

So are these two Hollywood heavyweights actually falling for each other?

Nope! All the action was just for their on-screen romance in the new comedy, "Four Christmases."