Back when cable was still pretty new, in the early '80s, that movie and "Moonraker" were the only things that played on HBO for MONTHS ON END.
My sister and I watched both movies over and over when we went to visit my dad, and we memorized them both, much to our mother's chagrin, considering how wildly inappropriate they were for preteens.
But "History of the World" was and is funny as hell.
Ah, yes, when HBO was brand new! I remember it well. My brother-in-law had stumbled across an old rounded-tube color TV. The signal scrambling of the time did not work on tube televisions, so we got HBO for free the whole six months the set lasted.
Since we were both unemployed at the time, we watched Monty Python and the Holy Grail every day until we had memorized every line! That's part of the reason I gave up, and enlisted in the USAF.