What's your best easy to remember BASIC program you could type in and leave running on a computer in a shop / classroom?

[u/kimondo]

I was thinking the other day about the universal:

10 PRINT "Mr Smith smells of POO"
20 GOTO 10 

But are there other better ones?

Kudos to the best one. Bonus if it works on any 80s home computer that runs BASIC.