Probably an old joke even then but I laughed and it still brings a smile – perhaps because that was long ago (seems longer every day) and reminds me of those days ….
The professor wrote 8 / 0 = "infinity sign" on the chalkboard and launched into a lecture on limits, defined expressions, undefined expressions, infinity, etc. The class took it all in, or so he thought. A few days later, he gave the class a test. One of the problems on the test was: 5 / 0 = ? Of course, one student gave the answer as “5 on its side” (you’ll have to use your imagination here since I can’t make a 5 in landscape orientation).
Thereafter, we always called the infinity symbol the “lazy eight”.
Well, it was funnier when the characters could be drawn on the chalkboard.