Had exactly the same thing happen when I was in the local village hardwear shop and I bought 12m of chain, the little old man said "its rather a lot, what are you going to do with it? chain up the dogs?" "No" says I "not ..the dogs ....the other half". Old lad behind the counter grinned at me and has grinned at me every time I have seen him since!
Edited to say - it was to chain up the dogs but I thought it would be nice to cheer up an old lad that has a woman come into his shop about twice a year.