Why do I need to know être à côté de la plaque?

Because this is the perfect expression for your co-worker who keeps going off topic.

What does it mean?

Être à côté de la plaque – usually pronounced eh-truh ah koe-tay deh lah plack – which translates precisely as “to be next to the plate,” but in practice is used to mean “off mark” or “to miss the point.” 

This expression is used when someone is mistaken – whether purposefully or otherwise. For politicians, for instance, they might be à côté de la plaque to purposefully evade answering a question in its proper context. For others, this phrase is more commonly used to just describe a moment where someone says something ‘out of left field,’ that misses the context or point of the conversation and is out of place.

This expression likely finds its origins in the world of railroads. For a train to change direction, a thick plate had to turn. In the event of a wrong manoeuvre, the train could wind up next to the plate, or rather –  next to the rail, meaning off track. 

One can be a little off mark (un petit peu à côté de la plaque) or extremely mistaken (complètement à côté de la plaque).

Use it like this

Sa réponse au test était à côté de la plaque. Il a commencé à parler de la guerre civile alors que la question portait sur la guerre révolutionnaire. – His answer on the test was off mark. He started talking about the civil war when the essay question was about the revolutionary war. 

J’ai l’impression qu’elle est toujours un peu à côté de la plaque pendant la réunion du matin. Comme aujourd’hui, elle a complètement mal compris le client. – I feel like she is always off point during the morning meeting – like today she completely misunderstood the client.