I never owned a C64, but I would always find them on display in department stores and type something like:
10 PRINT "Some derogatory comment"
20 GOTO 10
... and walk away.
Also, when I see the cassette, I remember (maybe correctly) that the electrical interface to these was basically a 300ish baud modem. Instead of transmitting the audio over phone lines, they just saved it as audio on a cassette. If you have one of these computers today, it would be interesting to see if you could replace the cassette player with the modern version, an MP3 player (that also records). The C64 would convert bits to audio, that the MP3 player receives and converts from the audio back to bits to be stored. The irony would be deafening.
Indeed you can run from an MP3. I have some of the audio on a CD that I connected to my sinclair 48k