This is a scene from the movie Synchronicity.
Jim: Was I playing the beard tonight?
Abby: Why do you ask?
Jim: Well, either you came to the lab with Klaus or you got there through the wormhole.
Abby: I did arrive with Klaus. But I'm leaving with you.
I am not sure what "playing the beard" means in this context, and it appears to be a total non-sequitur. It doesn't seem to be idiomatic. I can only think of it being sort of a reference to Jim being a facade/playing a role for Abby.