She: Hi there, I'd like to buy new cartridges for my printer.
He: What kind?
She: I've written the brand and make down.
She hands him the note.
He: Ok, we have those in stock, how many to you need?
She: Er, two?
He goes off and gets her two cartridges with black ink and pops them on the counter.
She looks at the boxes.
She: No, no, I meant two of each.
He: Two of each?
She: Yes, two black ones and two white ones.
He looks at her. Silence.
She clarifies: It's a black and white printer.
He without flinching: You're printer can only hold one cartridge, Miss.
/Mrs B ROFL