I swear this is a true story, one that I delight in telling whenever the person it concers is around:
A friend of mine once went to the local store for some vasaline, because he had dry lips. When he was heading out of the house he called to his flatmate asking whether the flatmate wanted him to pick up anything from the store, and the flatmate said that yes, he was running low on condoms so could my friend pick up a box? Exactly who asks their friend to do this I'm not sure, but that's not the point. Anyway, my friend picks up the vasaline and condoms at the store and thinks to himself 'you know, it's fairly embarasing visiting the store just for this. I'll pick up something else too,' so he grabs the nearest item and heads for the checkout.
Arriving at the checkout with a tub of vasaline, a box of condoms and a cucumber, he realises that he should have put some thought into the third item.