His dad sends him to the shop to ask for red and white striped paint, which doesn't really exist as the paint would mostly mix together in the tin and make some badly mixed pink paint. The employee in the shop sees this is a gag and asks a follow up question: would he like the paint to be striped vertically or horizontally? So they are on the way back and only *then the realisation dawns on them that this is a massive wind up, which sparks a rage large enough to break the door.