Travis Bickle: [Into the mirror.] You talkin' to me? You talkin' to me? You talkin' to me? Then who the hell else are you talkin' to? You talkin' to me? Well, I'm the only one here. Who the f**k do you think you're talking to? Oh, yeah? Okay! [whips out gun.] Huh?
When Travis is with the gun salesman, he is trying out the black gun. You see a close up shot of him holding the gun with his arm outstretched with his jacket on. In the very next shot (no time has elapsed) his arms are at his side and his jacket is now completely off.
Director Martin Scorsese makes more then just a cameo in this film, he's the passenger that sits with Travis talking about how he's going to kill his wife for cheating on him with a black man. He's credited as "Man Watching Silhouette".