MISCHA Barton had an awkward run-in with ex-boyfriend Brandon Davis at the pre-Halloween party thrown by DGI Management’s Yoni Goldberg on Mercer Street last Friday. “They saw each other and then spent the whole night on opposite ends of the party,” laughs a spy. “They didn’t seem interested in saying hello, and Mischa appeared a little wobbly.” Barton and Davis split in 2005 after more than a year together, and supposedly “remain good friends.” But maybe not.