This is a true story - I know the lady in question:
A young lady was at a nightclub with friends when a bloke approached her, looked at her and said, "32C". The lady, thinking he was referring to the size of her bust was quite indignant and replied, "No, I'm a 34B, not that it's any business of yours".
"Not your bra size," said the guy, "I meant you used to get on the 32C bus to Chelmsford every morning."