Not know your arse from your elbow

Pro Tip 1/3

This phrase is very informal and often considered rude or unprofessional.

In a casual conversation, someone might laugh and say, 'I don't know my arse from my elbow in the kitchen.'

Pro Tip 2/3

Predominantly used in the UK, this phrase may not be well understood elsewhere.

When I studied in the UK, I heard someone use 'doesn't know his arse from his elbow' and had to ask what it meant.

Pro Tip 3/3

The phrase is used to strongly emphasize a person's lack of knowledge in a specific area.

He tried to fix the car himself and ended up breaking it more—he clearly doesn't know his arse from his elbow.