When you have to phone customer service and your assigned customer number has more digits in it than the US national debt.
I had a related one today where the serial number on the product I had called support for was so small I - literally - needed a magnifying glass (yes, I do have one on my desk!) in order to read it! It was also very long.
No doubt with lots of low resolution and font caused ambiguous characters like 0 and O, 1 and l 5 and S.