Holdaway's an experienced guy when it comes to undercover work. He's assigned to mentor Orange (Freddie) through the process of infiltrating Joe Cabot's gang. He definitely has some attitude and he tries to impart it to Freddie through the commode story. He lets Freddie know that he's got to be a good actor to pull this off, like Marlon Brando.
Whether or not Holdaway wrote the bathroom story himself, he certainly seems to know what he's talking about when it comes to impersonating a marijuana-dealing thug. With his guidance and a little help from everyone's favorite snitch Longbeach Mike (we're still waiting for the spinoff TV show), Freddie's able to get the job that he'll really regret in a few days.