Remember, that's not an out-take; that's from the actual episode. God only knows what was in the takes that the director (James Burrows) didn't use. However, a Kaufman fan left this stirring defense as a YouTube comment:
What do you mean, unrehearsed? This is a perfect and brilliant performance! It's Latka who doesn't know what he's talking about, not Andy!
By the way, I've always been skeptical of the idea -- promoted in books about Kaufman and in the movie Man on the Moon that Kaufman had contempt for Taxi. Certainly he didn't want it to be seen as his main job, which was why he asked for (and got) permission to be absent from several episodes each season. And like many comedians who incorporate their material into sitcoms, he probably felt that Taxi was eating up his own material, co-opting his Foreign Man character and making it harder for him to do that character as part of his own act. But Kaufman, as far as I know, didn't bash the show in public at the time (there were a number of people in the '70s and early '80s who did go public bashing the shows they were on), and when the show was about to be canceled in 1983 he helped promote it. I just think it's wishful thinking on the part of his fans to believe that he really hated his entry into Mainstream Culture, but I'm not sure if it's true. Maybe I'm wrong. But at least he, unlike Jeff Conaway, wasn't dumb enough to actually leave Taxi.
Update: Commentators dispute my interpretation of this scene:
Sorry, I don't see the slightest shred of what you're talking about here either. I don't see anything that looks remotely unrehearsed on Andy's part. It's got that naturalistic, halting, stumbling verisimilitude that made Latka/Foreign Man so effective and charming. The "building list" concept is clearly a comedic mainstay, but that doesn't mean Latka should perform it like Henny Youngman. To my eye as well, it is indeed Latka who doesn't know what he's talking about, not Andy.