There’s no absolute proof but brilliant Los Angeles pop culture historian Domenic Priore believes this 1966 commercial to be the work of a young pre-Monty Python Terry Gilliam. I say it’s true. (Oops, it’s not. See below…)  Gilliam did after all attend high school in my beloved San Fernando Valley and worked at Carson Roberts advertising agency (along with Pet Sounds lyricist Tony Asher) in Los Angeles before finding his ultimate destiny in the U.K. There is unfortunately no official record or listing of Gilliam’s early TV commercial work, though there are doubtless many more such examples out there.
 

 
Update: Terry Gilliam’s co-worker at Carson Roberts, one Mike Salisbury has claimed creator-ship of this clip. He says: ”...Ed Ruscha worked there also. One of the first TV spots I did was there, for Baskin Robbins ice cream . Terry Gilliam and I worked on some things together but this one I created, wrote and animated. They gave us a lot of freedom. (it was a fun place to work—the in-house producer was the model for Mr. Magoo.)...” Also this from DM facebook friend Susan Pile: This direct from my pal TG: “...I had nothing to do with the commercial. And no idea who might have been the clever bastard. I’m up to my neck in my first opera: Berlioz’s The Damnation of Faust. All foolishly backed by the English National Opera. Luckily I’m surrounded by real pros that are keeping me from drowning….”  So there ya go !