My wife was supposed to put five candles on our daughter's birthday cake, but she blew it.

（子供の誕生日のケーキにろうそくを５本立てるはずだったのに、妻がだいなしにしちゃったんだよ。）
　NHKテレビ「ニュースで英会話」のだいぶ前の放送で "blow" を取り上げた時の会話例。

• blow it という形で「台無しにする」という意味（to spoil your chance of achieving something you want because of something you do or say）。ここでは会話の相手の日本人がろうそくを間違えて吹き消した（blew them out）のかと勘違いして、「また火をつければいいじゃない」と返す。私も最初そういう意味かなと思った。
  • She was hoping for promotion but she blew it when she got pregnant.
  • They want to publish his autobiography so let's hope he doesn't blow it by arguing with the publishers.
  • Most people think Congress blew it on the environment by not acting quickly on the president's proposals.
  • I have a job interview tomorrow.--Well, don't blow it.
  • I was late for the job interview and that blew it for me.
  • They should have won the game but they blew it.
  • You've got a great future ahead of you. Don't blow it.
• blow it という形でなくても、後ろにchanceやoppotunityという語を伴って、同じように「チャンスを台無しにする、ふいにする」という意味で使う。
  • He blew an opportunity to make a lot of money in the stock market.
  • I blew my chance for a big promotion.
  • We've blown our chances of getting that contract.