Can anybody identify the song played by the guy on the guitar?

There is a scene partway through the movie where a guy is about to hook up with the hippy chick. Before they do, they sit and talk on the couch and do some cocaine while he plays the guitar very briefly (the music fades into the background behind their dialogue).

When he first starts playing, there is a riff he plays with a little slide lick in there that just sounds so good. I'm not sure if this is a real song he's playing, or whether the actor was just improvising a tune for the sake of the scene.

If anybody has this information it would be greatly appreciated :)