Why do I need to know purée?

It's a swearword you can use in front of basically anyone.

What does it mean?

As a swearword, purée falls among the really harmless insults that you may use as you please.

Purée ! – Mashed potato!

It is kind of like saying 'oh sugar!' if you drop a vase in front of your kids. Even an old, posh French lady could probably hear you exclaim purée without frowning.

When can I use it?

Whenever!

Use purée like you use putain – which French people tend to do constantly (read more about putain here) – just without the fear of offending someone nearby.

Tu as vu l'heure? Purée, on est en retard – Did you see the time? Shoot, we're running late

Purée, il pleut ! – Oh darn, it's raining!

Purée, on a pas fait assez de purée – Oh sod it, we didn't make enough mashed potatoes.

Another French variant is punaise, 'darn' it', or the funny-sounding saperlipopette, which according to an online dictionary is an “ancient term used to express astonishment”. 

Any other options?

Don't forget that purée really refers to a delightful side dish that is mashed potatoes. Although the most traditional version is crushed pommes de terres (potatoes) mixed with a generous lump of butter, purée technically means “mash” and you can use in front of all mashed veggies:

Purée aux épinards – mashed spinach

Purée de carotte – mashed carrots

Purée de pois cassés – mashed peas

Or (personal favourite) Purée aux truffes – mashed potatoes with truffle oil.